Hypothesis vs Theory

a hypothesis is an UNTESTED idea or theory based on observations

predictions from a hypothesis need to be tested by experiment and may then be accepted as a proven THEORY by the scientific community.

if a reliable experiment does not support a hypothesis, the hypothesis must be changed. This also applies to accepted theories.

Precision vs Accuracy

… Precise measurements are ones in which there is very little spread about the mean value.

An instrument which can measure smaller intervals (a higher resolution) will often give more precise results.

… A measurement result is considered accurate if it is judged to be close to the true value.

Taking a mean of several results will usually increase the accuracy of the measurement.

Types of Error

… A random error is a variability in the measured value which cannot be controlled. Taking an average from several repeat measurements will reduce the effect of random errors.

… A ‘systematic error’ occurs when all the measurements are ‘out’ by a constant amount due to an incorrect callibration or consistently wrong measurment method.

Not zero-ing a balance correctly would result in a systematic error.

Motion

… What are the standard units used for the quantities:

speed?

time?

distance?

acceleration?

… The velocity of an object is its …?… in a certain d…?… Velocity is therefore a type of v…?… because it has both size and d…?…

… What is the difference between a vector and a scalar? Can you give some examples of quantities for each type?

… The gradient of a graph is the …?.. of the line.

… To find the gradient of a straight line, draw a large …?… under the line and measure the …?… and the …?… You can then use the formula to calculate the gradient, which is …?

… In a DISTANCE-time graph, a straight line going up or down at an angle means…?

The gradient (slope) of this line represents the …?… of the object. The steeper the gradient, the …?… the object is travelling.

… In a SPEED (or velocity) – time graph, a straight line going up or down at an angle means…?

The gradient (slope) of this line represents the …?… of the object.

… Negative acceleration is called d…?… (i.e. slowing down). How would you recognise positive and negative acceleration on a distance-time graph or a velocity-time graph?

… The formula for acceleration is given by:

a = (v – u) / t or v = u + at (“vuat”)

What quantities do these letter symbols stand for, and what units do they have?

… In a velocity (or speed) – time graph, the DISTANCE travelled can be found by…?

‘Suvat’ equations for working out constant acceleration problems using L.E.S.S. (List – Equation – Solve – State)

… Often a labelled diagram helps to ‘digest’ the question at the start (neat and large please!)

… Then make a suvat LIST of data with the units. For example:

s = 20m

u = 0 m/s

v = 36 m/s

a = 2.5 m/s²

t = (not given, so not needed)

Watch out for when a question states that an object starts moving “from rest”… then you know that…?

… Equation: Select the appropriate suvat equation which fits your list.

a = (v – u) / t

v² – u² = 2as … For the above data list, this equation fits.

… Solve by substituting the numbers in.

… State the units of the answer at the end (they should match the units in your data List).

Forces

… The three effects of forces are…?

… Forces come in two main families – contact and non-contact forces. Can you give three examples of each type?

… Air resistance creates a d..?… force on moving bodies

… Forces are types of VECTORS – this means that d…?… is important and the forces can be added (if going in the same direction) or subtracted (if going in …?… directions) from each other.

… What is the difference between a vector quantity and a scalar quantity? Can you give three examples of each?

… The r…?… force (unbalanced force) is what you’re left with when you combine all the forces acting on an object into one.

… A resultant force will always cause a body to …?…, or change in …?…

… When adding vectors such as forces, make sure that you place each vector arrow in a ‘chain’, one after the other. Then the resultant force is the vector arrow which joins the stating point with the ending point.

Newton’s First Law

… If the resultant force is ZERO then an object will either be at …?…, or it will be moving in a …?… line at a constant …?… . (This is called Newton’s FIRST law of motion)

Newton’s 2nd law of motion

… The acceleration of a body is proportional to the …?… force acting on the body, but inversely proportional to the body’s …?…

The equation is:

a = …?…

… We worked through a calculation using F = m x a.

Remember to follow the Diagram – List – Equation – Solve – State process for your calculations with forces.

… Newton’s 3rd law: Forces always come in e…?… and o…?… pairs which must be of the same …?… (e.g. The gravitational force of the Earth on a ball downwards is equal to the gravitational force of the …?… on the …?… upwards!)

… Upthrust is the force which makes objects float in liquids, or makes hot air balloons float in air. (It is due to pressure differences acting on the object)

… Acceleration is measured in units of metres per second squared (m/s²)

… Three factors that will affect a vehicle’s thinking distance are…?

… Three factors that will affect a vehicles’s braking distance are…?

… How does the initial speed of a vehicle affect the

Thinking distance?

Braking distance?

… The faster an object moves through a fluid, the …?… the friction force (also called d..?…) that tries to slow it down.

Ie

… Weight is the force (measured in units of …?…) that gravity exerts on an object’s m…?… due to the pull of …?…

… Weight has units of …?…

… In physics we always use the units of …?… for mass.

… The strength of gravity depends on the ..?… of the planet (and how densely it is packed). This means that 1kg on the Moon weighs …?… than 1kg on the Earth.

… What are the units of the strength of gravity, g?

… 1kg on Earth has a weight approximately equal to …?… newtons.

… The weight of an object can be calculated using the equation…?

… Why is it (technically) incorrect to say, “the weight of an apple is 100 grams” ?

… What is the weight (on Earth) of a 550kg car? Remember to use L.E.S.S. (List – Equation – Solve – State) for your calculation.

… Terminal velocity is when an object moves at a …?… speed because…?

… If the effect of air resistance can be ignored (e.g. streamlined objects), then what can you say about the MOTION of a small mass and a large mass if they are dropped from the same height at the same time? (This was demonstrated by Neil Armstrong when he dropped a hammer and a feather on the moon)

… When a spring is pulled, the e…?… is proportional to the …?… applied. This is called …?…’s Law.

… F = k x e, where k is called the ‘spring …?…’ and e is the …?…. (Watch out that the units agree in questions, as sometimes you may need to convert mm or cm into m).

… Spring extension is the spring’s INCREASE in length, not the actual length of the spring 🙂

… The accuracy of a spring force-extension experiment can be increased by taking r…?… readings and calculating an …?…

How could you avoid parallax error when taking a reading of the spring length?

… Springs can be combined in series and parallel.

With two identical springs in series, the spring constant (stiffness) halves.

With two identical springs hung in parallel, the spring constant doubles.

… For a graph of force applied to a spring vs. extension of the spring:

- the limit of proportionality is located at the point where…?
- the elastic limit is when …?… starts to occur. It is usually close to the limit of proportionality.

… What is the difference between elastic and plastic (inelastic) deformation?

… Vocabulary is really important when answering questions on forces and motion – try to use as many relevant keywords as possible (acceleration, deceleration, resultant force, mass, weight, constant speed, upthrust, at rest…).

.. Answering Force and motion describe / explain type question. Here is a strategy you could use for these types of question:

- describe what is happening to the object’s VELOCITY (increasing = accelerating, constant or decreasing = decelerating)
- link this to the FORCES acting on the object (balanced so resultant force = 0, or unbalanced so there is a resultant force)
- are any forces increasing with TIME? For example, air resistance might be increasing because the object is moving …?… How does this affect the resultant force and the acceleration?

Note that steps 1 and 2 might be the other way round, so comment on the forces first, then how this affects the velocity 🙂

Keep ‘drilling down’ to expand your answer by using linking phrases such as,

‘this means that…’

or

‘…because…’

Work Done, Energy and Power

… Work done means “e…?… T…?…” from one form to another. It is measured in units of …?… and the quantity can have the symbol W or E.

… Energy cannot be …?… or …?… This is known as the ‘Law of Conservation of Energy’.

… Work done (energy transferred) = force x distance moved (in the direction of the force):

W = F x s.

The units for W, F and s are…?

… When you lift an object through a height, your muscles transfer …?… energy into …?… …?… energy. This means that your muscles ‘do work’.

… When an object falls, gravity does work by transferring …?… …?… energy into …?… energy.

… An object is thrown up into the air and starts with 0.5J of kinetic energy. This energy then transfers into …?… …?… energy. What can you say about the object’s energy when it has reached the highest point (assuming air resistance is negligible)?

… Friction transfers …?… energy into …?… and …?… energy

… The energy stored in a spring when it is stretched or compressed is called …?… …?… energy. The equation for this stored energy is:

Ep = ½ke²

… Power is the rate of doing …?… (or the energy transferred per …?…).

… Power = …?… / …?… (P = E/t) and is measured in units of…?

… Gravitational potential energy, E = m x g x h. Remember that g is the …?… field strength which has units …?…

… ‘Potential’ means ‘easily …?…’, e.g. chemical potential energy in your …?…

… Always work in ‘base’ units, e.g. kg (not grams), m (not cm). Sometimes you will need to convert data in the question into base units.

… Kinetic energy = ½mv². This means that if you double your speed, then you will …?… your kinetic energy. This is an important factor in car safety – why?

Momentum

… The momentum of a moving object tells us how difficult it is to make the object …?…

… Momentum = …?… x …?… and is measured in units of…?

… Momentum is a vector, which means that a forwards momentum might be positive, but a backwards momentum would be …?…

… The ‘Law of Conservation of Momentum’ in an explosion or collision says that:

The total momentum of all the objects …?… = the total momentum of all the objects …?…

This law is true as long as there are no external …?… acting on the objects (such as friction).

… It can be very useful to draw a ‘before and after’ diagram showing the masses (in kg) and velocities (in m/s) of the objects. Call the velocity you are looking for ‘v’.

A before and after diagram makes it much easier to see the situation and to show your calculations for “total momentums before = total momentums after”

… Impulse is another name for the change of …?…

… Average force applied = change in momentum / time force is applied

or F = (mv-mu)/t

… The longer the time of a collision, the …?… the force exerted. How do car crumple zones make use of this idea?

… Knee pads reduce injuries because:

1) the time of impact is increased

2) this means that the rate of change of momentum is decreased

3) which reduces the average force applied to the knee.

… Why is it easier to hammer a nail into a wooden block using a metal hammer rather than a rubber hammer?

… Why do seat belts and air bags help to reduce injuries in a car crash?

… You can also explain how crumple zones, seat belts and air bags work by using the ideas of Newton’s second law:

Crumple zones increase the …?… of impact,

This causes the deceleration of the car and its occupants to be …?…,

This means that the force that created the deceleration must have been …?… because F = m × a

Therefore reducing damage or injuries.

Static electricity

… Friction causes …?… to move from one material to another (usually insulators). This means that one material can become negatively charged, and the other will become …?… charged by an …?… amount.

… When electrons move, the positive …?… are left behind (as they cannot move in a solid).

… Different insulating materials will charge either positively or negatively. For example, polythene tends to become negatively charged, whereas Perspex tends to become positively charged when rubbed with wool.

… A positively or negatively charged object can i…?… a charge in another object by attracting or repelling electrons at a distance.

Use this idea to explain why a balloon rubbed with wool can then be ‘stuck’ onto the ceiling?

… Explain how the static electricity is used in the following applications:

– Spray painting of a metal object

– Reducing dust emissions from a chimney using a ‘p…?…’

– Earthing an aircraft refuelling pipe to avoid an explosion

– In a photocopier

… Applications of static electricity include the following (watch the short videos to understand them better):

- Photocopiers use static electricity to duplicate an image: https://youtu.be/Sy5PPaxaBCI?si=xosgYQB8UiBmQ8px
- Chimney precipitators (to remove harmful gases): https://youtu.be/O1MpaGZnlEE
- Earthing an aircraft refuelling pipe to avoid an explosion: https://youtu.be/yifqs1NE4Ew?si=kI7bXiflclXgLthz
- Spray painting: https://youtu.be/HvsT9XZLRlA?si=WcZZ9X510nF-s42p

Electrical circuits

… We can use a model to help us understand electricity:

Battery or cell = hot water boiler and pump

metal wires = pipes

charge = water

current = flow of water, e.g. through the pipes

voltage = temperature or pressure of the water.

potential difference (voltage drop) = temperature or pressure drop of the water when it goes through a component.

… An electrical current in a conductor (such as a m…?… wire) is a flow of charge (electrons).

… A potential difference across a component will cause a current to flow through it.

… What is the symbol and unit for charge?

… A current is a flow of …?… What is the symbol and unit for current?

… A current will flow in a c…?… circuit.

… Which side of a cell or battery is the positive?

… Conventional current vs electron flow… Which direction from a battery does each of these flow?

… The flow of charge in a certain time: Q = I x t. What quantities do these symbols represent? What are their units?

… Calculations using Q = I x t. Well done for spotting that we needed to convert the units in our ‘List’ of data to start with.

… Potential difference (or voltage difference) across a component is the e…?… transferred by each Coulomb of charge as it flows through the component.

Potential difference is measured in units of …?… You can also think of potential difference as the electrical ‘pressure’ that pushes charge around a circuit (it causes a current to flow).

… The voltage at any point in a circuit tells us how much …?… each coulomb of charge has at that point, usually relative to 0V (the negative side of the battery).

… Energy transferred equation: E = V x Q. What quantities do these symbols represent? What are their units?

… An electric field is an area in space in which a c…?… experiences a …?…

What would the electric field line pattern look like around a positively charged sphere?

… Cells can be connected so that they ‘push’ in different …?… . This means their potential differences can be combined by a…?… or s…?… them.

… You asked a very good question about how do the electrons (or positive charge ‘holes’) know that they must share their voltage over components that are connected in series.

To answer this question, we discussed an analogy using the idea of a ball rolling down a hill. This was nearly correct… however, for a 1-component circuit, the hill actually needs to be split up into three sections:

- The first section = wire. This has a very slight slope downwards and so the ball doesn’t lose very much potential energy.
- The second section = component, for example a resistor. This has a very steep slope downwards so that at the end of the component most of the ball’s potential energy has been transferred.
- The last section = wire again. This, once again, has a very slight slope eventually leading down to the ground level.

The steepness of the slope in this analogy is actually the electric field strength in the wire. A strong electric field will apply a large force on a charge, making it move faster.

The electric field ‘arranges itself’ depending on the resistance of each component (and sections of wire) in the series circuit.

So if we have two identical components connected in series, the slope (the electric field) in each component will be about half as steep compared to the slope in just one component.

Series and parallel circuits

… A series circuit only has one ‘loop’ – the components are placed one after the other. Ammeters should be connected in …?… with a circuit to measure the current flowing.

… The current in a series circuit is c…?… at every point. This means you can connect an ammeter at any position in a series circuit.

… In a series circuit, the potential difference across the components is s…?… depending on their resistances. Higher resistance components are more ‘greedy’!

… A parallel circuit has more than one ‘loop’. Voltmeters should be connected in …?… to measure the potential difference across a component.

… In a parallel circuit, current splits at one or more junctions. The potential difference across components connected in parallel is always the …?…

How to analyse a parallel circuit to find currents and potential differences across components:

… 1. The sum of the currents into a junction = sum of the currents out.

… 2. The sum of the potential differences dropped across components in any particular series loop = the potential difference of the supply

No.2 means that you can consider just ONE series loop and ignore any parallel branches to create an equation which you can solve.

… How to set up a series circuit to measure the potential differences across a lamp and the current flowing in the circuit.

Resistance

… The resistance of a component tells us how easy it is for charge to flow through it. A component with a high resistance will only let a small current flow through it.

… Resistance, R, is measured in units of …?…, symbol …?…

… The resistance of a component = potential difference across it ÷ the current through it:

R = V / I

or you can use the rearranged form:

V = I × R

which is much easier to remember.

… The total resistance of resistors in series is calculated by…?

… When resistors are combined in parallel, the combined resistance is always …?… than the smallest resistor value.

This is because the parallel circuit provides another path for current to flow along. Think of another lane opening on a motorway – more cars can flow past per second and so the total resistance must have fallen.

… The formula for calculating resistors in parallel is…?

… A voltmeter has a VERY high resistance so that hardly any current flows into it. This is so that it doesn’t affect the circuit.

… An ammeter has a VERY low resistance so that hardly any potential difference is dropped across it (so that it doesn’t affect the circuit).

… A thermistor’s resistance will …?… when it is heated.

… The resistance of a light dependent resistor (LDR) gets …?… when more light is shone on it.

… In an electrical circuit, the …?… through a resistor is directly …?… to the potential difference across it (as long as the resistor is held at a …?… temperature. This is called …?… Law.

It means that if you double the potential difference (voltage) then the current will…?

… How to set up a series circuit to investigate the effect of current on the resistance of a lamp.

… What do the graphs of current vs potential difference (I-V) look like for:

- a resistor?
- a diode?
- a filament lamp?

… What happens to the current in a circuit if the resistance in the circuit decreases?

… The resistance of a filament bulb increases as it gets hotter because…? (Remember to mention vibrations, metal ions, electrons, resistance…)

… A diode is made from a junction between two different types of semiconductors. Conventional current can only flow in one direction (the direction of the arrow in the diode symbol).

… Diodes are useful for protecting sensitive electrical circuits from reverse voltages (e.g. putting the batteries in the wrong way round!) and for converting AC current into DC.

… A transistor is made from two types of semiconductor materials (p type and n type) in a PNP or NPN ‘sandwich’. A small current flowing into the base of the transistor (the middle layer) enables a much larger current to flow through the transistor sandwich. Transistors are therefore types of sensitive electronic switches and can also be used to amplify signals (analogue or digital).

… A potentiometer is a type of variable potential divider circuit.

A slider moves up and down a fixed resistor, which effectively divides the resistor into two resistors above and below the slider contact.

Remember that a power supply’s potential difference will be shared across the two resistors according to the ratio of their resistances.

This means that the slider can ‘select’ different voltages depending on its position.

… There is an increasing use of LEDs for lighting as they use a much smaller …?… than other bulb types and have a much longer …?…

However, LEDs cost …?… than filament bulbs or CFLs (compact fluorescent lamps)

… How does a filament bulb, fluorescent bulb and an LED compare for:

cost to buy?

Energy efficiency?

Average life?

Household electricity and safety

… Power sources that constantly change the direction of current flow are called …?… …?… supplies.

… What is the formula that links the time period of a wave (T) with its frequency (f)?

… The time period of a wave could be measured as 20ms. What does the ‘m’ in ‘ms’ stand for?

… The frequency of a voltage supply tells us how many o…?… happen each s…?… , and is measured in units of …?…

… In the UK, ‘the mains’ has a frequency of …?… It has an effective potential difference of …?…V, but a peak voltage of …?…V

… What are the names and colours of the wires in a 3-pin mains plug?

… The materials Copper, plastic/rubber and brass are used in a 3-pin mains electricity plug. Name the parts of the plug for which these materials are used, and explain why their properties are suitable for each part.

… How does a fuse work to protect an appliance from high currents caused by faults? Why are electrical faults dangerous?

… The correct fuse to use in an appliance should be rated at a slightly higher current than the normal operating current. For example, if a kitchen appliance draws 4A in normal operation, then a 5A fuse is appropriate.

The appliance would still work normally with a 13A fuse, but this is too high as it would take much longer to melt if there was a fault.

… How does the earth wire work with the fuse to protect against an electric shock in appliances with metal casings? Make sure you can explain the steps starting from, “if a fault happens in the appliance where the live wire touches the metal casing…”

… Appliances that require high currents (like toasters or kettles) need THICKER wires because…?

… When a current flows through a resistor, the temperature of the resistor …?… because work is being done by the …?… (measured in coulombs) as it transfers energy from …?… to …?… energy.

… What do the symbols represent in the equation P = I x V ? What is the unit of each quantity?

… Combining P = I V with V = I R gives us another useful equation:

P = I²R

How does this equation explain why it is better to transmit electricity across the country at a very high voltage and low current?

… The power rating (units of …?…) of an appliance tells you how much …?… is transferred in each …?…

… Identifying components of a mains electricity plug, including live wire, neutral wire, earth wire, fuse, cable grip and insulation.

… How to wire a mains electricity plug and which safety points to look out for.

… Double insulated appliances do not need an earth wire because…? These appliances are labelled with…?

… Residual current circuit breakers (RCCBs) are alternatives to fuses – advantages include faster response time, higher sensitivity and no need to replace if they ‘trip’, just reset.

… RCCBs work by comparing the input current with the output current. If the currents are different it will ‘trip’ which disconnects the live supply and makes the appliance safe.

RCCBs are usually be used alongside another type of circuit breaker which will disconnect the live supply if the current becomes too HIGH.

Here is a useful page about how the electromagnets inside an RCCBs operate: http://www.gcsescience.com/pme9.htm

Radioactivity and the nucleus

The ‘plum pudding’ vs the ‘nuclear’ model of the atom

… Rutherford’s gold foil experiment: Rutherford shot …?… particles at …?… foil and observed that:

1. Most went straight through with no d…?… This meant that the atom is mainly empty space.

2. A small proportion were deflected through small angles. This suggests a nucleus which has a …?… charge (because alpha particles are positively charged and would be repelled away from a positive nucleus).

3. A very small number of alpha particles rebounded through a very large angle. This means that the size of the nucleus must be very …?… and it must have a large …?…

… The nuclear model of the atom: an atom is mostly empty s…?…. The nucleus contains most of the atom’s m…?… and is a tiny p…?…-charged point at the c…?… of the atom. Electrons orbit on the outside.

… Rutherford, Chadwick and Niels Bohr discovered which features of an atom’s structure?

… What is the relative mass of:

- a proton?
- a neutron?
- an electron?

… If an atom loses or gains electrons, then it becomes charged, because…?

When this happens, the atom has become an …?…

… What are alpha, beta and gamma radiations?

… Alpha radiation is made up of 2 pairs of particles, which are…? This means that an alpha particle is the nucleus of the element …?…

… Beta radiation is a high speed …?… that is ejected from the unstable nucleus. Where does this particle come from?

… Gamma radiation is an e…?… wave, so it is not a particle at all.

… Background radiation comes from many sources including natural sources such as:

r…?… (people living in Cornwall are exposed to more radiation due to the granite there),

food & drink

cosmic rays

and man-made sources, such as:

hospitals

n…?… w…?… .

… Radioactive decay of the nucleus is a r…?… process (this means that we don’t know when a single radioactive nucleus will decay). However, if you have enough nuclei you can predict how many will decay in a certain time on average.

… Gamma rays have the shortest wavelength of the electromagnetic spectrum

… Note that if a material is exposed to alpha, beta or gamma radiation, some atoms will be ionised. These ions may go on to react chemically but will NOT be radioactive themselves.

… Radiation dosage is measured in Sieverts. On average in the UK a person receives 2.7mSv due to background radiation.

… Nuclear radiation can be detected using:

a G…?…-M…?… tube connected to a counter.

a photographic film

a cloud chamber

The advantages and disadvantages of these methods of detection are…?

… Alpha, beta and gamma radiations can i…?… atoms of a material (they can knock electrons out of the atoms making them into charged particles called i…?…)

… An Isotope is a different form of the same element (same …?… number) but with different numbers of …?… (different mass number).

… …?… radiation is the most ionising and so can cause the most damage to living tissue.

… Nuclear decay equations – how the mass number and the atomic number change when a nucleus decays. Watch out for beta decay, which is when a neutron changes into a …?… and a high speed …?… which is ejected from the nucleus!

… When an nucleus decays by alpha or beta emission, we can say that the atom has t…?… to a different element.

… Balancing the numbers in a nuclear decay equation. Note that a beta particle is an electron with mass number …?… and atomic number …?… The numbers on the RHS must add up to the numbers on the LHS.

… The Ionising power, range and penetration properties of alpha, beta and gamma are…?

… How is alpha, beta and gamma radiation affected as each one passes through a magnetic or electric field?

…The half life of a radioactive isotope is the average …?… taken for …?… the number of its nuclei to decay.

… Half life is also the …?… taken for the COUNT RATE of a radioactive sample to …?…. Count rate can be measured by the ‘counts per minute’ clicks on a Geiger counter detector. It is proportional to the number of radioactive nuclei remaining in a sample.

… How can you calculate the half life from an isotope’s decay curve?

… If a radioactive isotope sample has a half life of 8 hours and the starting count rate is 1200 counts per second, how long would it take for the sample to decay to a count rate of 75 counts per second?

… We performed a simple simulation of radioactive nuclei using lots of dice and plotted a ‘decay curve’ (a nucleus decayed when any die rolled a ‘6’). We then calculated the half life of our ‘radioactive dice’!

… Radioactive isotopes which emit …?… radiation are used in a smoke detector. Explain what happens when smoke gets into the detector which causes the alarm to sound.

… Radioactive isotopes which emit …?… particles are used to monitor the thickness of paper or thin foil factories. How does this work?

… Gamma radiation can be used to …?… hospital equipment and kill bacteria in …?… to extend its shelf life.

… Tracers can be used in medicine, e.g. A gamma emitting isotope can be injected into the blood stream to check that organs are working correctly. Gamma isotopes can also be used to detect pipeline leaks as the gamma waves are able to penetrate through the soil to a Geiger counter detector. What length of half life should be used for these applications? Why?

Nuclear fission

… Fission can create a controlled chain reaction to power a nuclear power station.

… Fission is the splitting of a large nucleus such as u..?…-235 to release energy

… Daughter fragment nuclei are created which are radioactive and have a long h..?.. l..?.. of hundreds of years.

… The heat energy created by a fission reactor is used to boil water to make steam, which turns t..?… connected to electrical g..?…

… Fission also releases fast neutrons which can go on to fission other uranium nuclei if they are slowed down by a m…?… in the reactor core, such as w…?… or graphite.

… C..?… rods made of boron can be lowered into the reactor core to absorb excess n…?… created by fissions so that the chain reaction can be controlled.

… Fission equations (uranium-235 fissioning to daughter products and neutrons) and calculations to find mass numbers or atomic numbers.

… What are the advantages and disadvantages of using fission to generate electricity?

Fusion

… Fusion is when two light hydrogen nuclei collide and fuse into a heavier nucleus, releasing energy.

… To make this happen, you need huge t…?… and p..?…, such as found in a star!

… Stars create their energy by nuclear fusion of hydrogen nuclei.

… Man-made fusion is possible and has been done… but commercial energy production is many years away from becoming a reality.

Here’s an interesting video which explains how close we are to achieving fusion energy to power our homes :

https://youtu.be/ZW_YCWLyv6A

… What are the advantages and disadvantages of using fusion to generate electricity?

The life cycle of stars

For stars with a similar mass as our sun:

… Protostar (gravity pulls dust and hydrogen together, temperature and pressure rise.

… Fusion of hydrogen into helium nuclei (when the temperature and pressure are large enough)

… Main sequence star (several billion years)

… Red giant (it has run out of hydrogen gas and now fuses helium nuclei)

… White dwarf (a white hot lump of dense matter)

… Black dwarf (a cold lump of dense matter!)

Stars with more than 3x the mass of our sun will become red super giants (fusing together heavier elements than helium) and then explode in a supernova to form a neutron star, or a black hole if they are large enough.

… All the elements which are more massive than iron are created from fusion in a supernova explosion and spread over a huge area, which is called a nebula. This becomes a ‘star nursery’ for secondary stars to form in the same life cycle process.

… When dust and gas from a supernova are pulled together by gravity to form another protostar, ‘lumps’ of rock also form orbiting around the protostar. These are called planetoids – baby planets!

Here is a useful video on the life cycle of stars: http://youtu.be/PM9CQDlQI0A