Topic 10&11:Electrical Circuits and Static Electricty

Question 1

What is an electron?

Answer 1

They are negatively charged and are much smaller that neutrons and protons and their mass is negligible. They are found in shells at different distances from the nucleus.

Question 2

Why is an atom have a no charge?

Answer 2

Because the number of protons is equal to the number of electrons so the charges cancel each other out.

Question 3

Define what is meant by a ‘free electron’?

Answer 3

All metals have electron is shells around them with a weak attraction to their nucleus. They can easily be removed, so a metal wire can have many free electrons. E.g copper.

Question 4

In what way do electrons move around a circuit and why?

Answer 4

When a battery is attached to a wire the voltage ‘pushes’ the free electrons around the circuit. The electrons are negative do move towards the positive terminal of a battery. However the direction of the conventional current goes from the positive terminal to the negative terminal of the battery.

Question 5

What is a battery?

Answer 5

A number of electrical cells in series.

Question 6

What does voltage mean?

Answer 6

The difference in energy carried by electrons before and after they have flowed through a component. This is another term for potential difference.

Question 7

What is the difference between a series and parallel circuit?

Answer 7

In a series circuit there is just one route the current can take around the circuit.

In a parallel circuit there are junctions that allow the current to take different routes.

Question 8

Give an example of how series and parallel circuits differ:

Answer 8

In a series circuit lamps cannot be switched on and off individually and if one lamp fails then they all switch off. On a parallel circuit the lamps can be turned on and off individually and they do not affect each other.

Question 9

How is an electrical current measured and what are the units?

Answer 9

It is measure using amperes often shortened to amps (A). Can be measured by using an ammeter as it measures the amount of current passing through a component in a circuit.

Question 10

What is meant by current is conserved?

Answer 10

The amount of current leaving the positive terminal will be the same as the amount of current arriving at the negative terminal.

In a parallel circuit, current splits at junctions to travel along different branches but the total entering the junction is the same as that of leaving the junction.

Question 11

What must happen to a circuit for current to flow?

Answer 11

The circuit must be closed for electrons to flow all the way round and and to must contain a source of potential difference (such as a cell or battery).

Question 12

How does potential difference have an affect on the current?

Answer 12

The bigger the potential difference of a component the bigger the current.

Question 13

How does potential difference work in a parallel circuit?

Answer 13

In a parallel circuit the potential difference across each branch is the same. When there is more than one component in the branch of a circuit, the potential difference across all components add up to give the total potential difference provided by battery.

Question 14

What is potential difference/voltage measure in and how?

Answer 14

Measured Volts (V) using a voltmeter.

It is always connected in parallel to measure to measure the potential difference across the component of a circuit.

Question 15

What do moving charged particles form?

Answer 15

They form an electoral current.

Question 16

What is electrical current measure in?

Answer 16

Coulombs (C)

1 Coulomb is the charge that passes a point in a circuit where there is a current of 1 amp for 1 second.

Question 17

In metals what is the current?

Answer 17

In metals the current is the flow of electrons.

Question 18

What does the size if current in a circuit tell you?

Answer 18

The size of current at any point in a circuit tells you how much charge flows past Avicenna point each second. Electrical current is the rate of flow of charge.

Question 19

How can charge be calculated?

Answer 19

Charge (C) = current(A) x time(S)

It can also be written as…

Q = I x t

Q= charge
I= current
t=time

Question 20

How is energy transferred in a circuit? (Give an example)

Answer 20

A cell contains a store of energy ➡️ (energy is transferred to charge) ➡️ the charge can now transfer energy to the components in the circuit (it now has potential energy) ➡️ (energy is transferred from the charge as it moves through the lamp) ➡️the lamp transfers energy to surroundings by heat and light.

Question 21

What is meant by the potential difference of a cell?

Answer 21

The potential difference of a cell is the amount of potential energy the cell transfers to each coulomb of charge flowing through it.

There is a postnatal difference of 1 volt when there is a transfer of one joule of energy to each coulomb of energy. 1 volt = 1 joule per coulomb.

Question 22

How can energy transferred be calculated?

Answer 22

Energy transferred(J)=Charge moved(C) x potential difference(V)

E = Q x V

Question 23

What do wires and components need when there is a larger electrical resistance in a circuit?

Answer 23

They need a larger potential difference to produce a current through them.

Question 24

What is resistance measured in?

Answer 24

Resistance in measured in ohms ♎️

Question 25

How is the potential difference of a circuit calculated?

Answer 25

Potential difference(V)= current(A) x resistance

V= I x R

Question 26

How do resistors act in a series circuit?

Answer 26

When resistors are connected in series the total resistance of the circuit is increased because the pathway becomes harder for the current to flow through. Potential difference from a cell is shared between between the resistors but may not be shared equally. There will be a greater potential difference across resistors with higher resistances.

Question 27

How do distort act in a parallel circuit?

Answer 27

When resistors are connected in a parallel circuit the the total resistance of the circuit is less than the resistance of individual resistors this is because there are now more paths for the current.

Question 28

What does a variable resistor do in a circuit?

Answer 28

The variable resistor is used to change the current in the circuit. Measure,nets of current and potential difference are recorded and resistance in calculated.

Question 29

What happens to current when the potential difference across a fixed resistor is changed?

Answer 29

The current changes by the changes by the same percentage. These two variables are in direct proportion. This happens because the resistance stays the same.

Question 30

What does the potential difference across a filament lamp cause and how can this change with increased potential difference?

Answer 30

Potential difference in a filament lamp causes current to flow through it. The current causes the filament lamp to heat up and glow. The greater the potential difference, the more current flows so the brighter the lamp and the more heat it give out. However as it heats up the resistance increases.

This means when potential difference changes the current does not change by the same amount.

Question 31

What kind of resistance does a diode have?

Answer 31

A diode had a low resistance if the potential difference is in one direction but a very high resistance if it is flowing in the opposite direction. This means current can only flow in one direction.

Question 32

How does a Light Depend Resistor (LDR) resistance vary?

Answer 32

Has a high resistance in the dark and bu the resistance gets smaller when light intensity increases.

Question 33

How does the resistance of a thermistor vary?

Answer 33

They have high resistance at low temperatures but s temperatures increased resistance decreases.

Question 34

Why do circuits warm up?

Answer 34

Due to resistance when there is current flowing through the circuit.

Question 35

Why is energy transferred when current passes through a resistor?

Answer 35

This is because electrical work is done against the resistance. Energy is transferred by heating and the resistor becomes warm.

Question 36

Why is the heating affect not useful in circuits or plugs and wires?

Answer 36

Useful energy is being transferred from the circuit to the surroundings by heating and is then dissipated. The surroundings gain thermal energy.

Question 37

How can resistance be reduced in circuits?

Answer 37

Using wires made from metals with low resist me such as copper. Thicker wires also have lower resistance. Resistance can also be decreased by cooling metals so that lattice ions are not vibrating as much.

Question 38

What is the equation for electrical power?

Answer 38

Electrical power(W)= current(A) x potential different(V)
P= I x V

Or…

Electrical power(W)= current(squared)(A)x resistance (♎️)
E=I(squared) x r

Question 39

What is meant by mains electricity?

Answer 39

Appliances that use a lot of electricity use mains electricity. This is 230 volts in the UK.

Question 40

How does electricity reach our homes?

Answer 40

In a power station energy is transferred from a store of kinetic energy to by electricity. The electricity is carried to our homes through a network of wires and cables known as the national grid.

Question 41

What is direct current (d.c)?

Answer 41

Cells and batteries have a positive and negative terminal and the direction of the movement of charge stays the same.

Question 42

What is an alternating current?

Answer 42

Mains electricity is produced using generators that rotate, causing the direction of the current to keep changing. This means the voltage keeps on changing to. Reaching a peak voltage and then decreasing to zero. The cycle then repeats.

Question 43

What is the frequency of the mains supply on the UK?

Answer 43

50Hz.

Question 44

What is meant by the power rating of an appliance ?

Answer 44

The power rating of an appliance is measured is watts (W). A kettle with a power rating of 3kW transfers 3000J of energy per second.

Question 45

What does an Earth wire in a plug do?

Answer 45

Connects the metal parts of an appliance to a large metal spike of metal tubing that is pushed into the ground. This is for safety and has 0v.

Question 46

What does a neutral wire in a plug do?

Answer 46

This is the return path to the power station. If the circuit is correctly connected it is at a voltage of 0.

Question 47

What does fuse do in a plug?

Answer 47

It is a safety device marked with current it carries. Usually 3A 5A or 13A.

Question 48

What does a live wire so in a plug?

Answer 48

Connects the appliances to the generators at the power station. The voltage on this wire is 230V.

Question 49

What are the safety features of a 3 pin plug?

Answer 49

• switches are connected in the live wire of the circuit. When the switch is off no current can flow through to the appliance.
• a fuse is a tube with a thin wire inside. The current passes through the wire and the wire gets hotter. If the current exceeds a certain value the wire melts and the circuit breaks.

Question 50

Why is a fuse needed in a circuit?

Answer 50

If a faulty appliance draws too much current, it can cause over heating of the wiring in either the wall or appliance. This can cause a fires. The fuse stops this from happening.

Question 51

Why do the metal plants of plug need to be connected to the earth wire?

Answer 51

Of you touched the metal you might get a dangerous electrical shock.a current would flow through you into the ground.the earth wire enables the current to flow into the ground instead of through you.

Question 52

What is a circuit breaker?

Answer 52

They can alternate to fuses. They detect a change in the current and safely switch of the supply.

Question 53

What are 2 advantages of circuit breakers?

Answer 53

• once a fault is fixed they can be switched back on again, where as a fuse has to be replaced.
• some of them work very quickly, so can save lives. A fuse takes some time to melt and will not prevent you getting shocked if you touched a live wire.

Question 54

Why can plastics collect charge?

Answer 54

Because it’s an insulator so cannot conduct electricity. Other insulators include acetate and polythene.

Question 55

What happens when you rub an acetate rod against against a dry duster?

Answer 55

Electrons flow from the plastic onto the duster as the acetate has collected charge. since electrons have a negative charge the duster gains an overall negative charge and leaves the acetate Rod with a positive charge.

Question 56

What is static electricity?

Answer 56

When charge is not always able to flow away to the surroundings. Since everything has the same charge the objects repel each other e.g causing hairs to stand up.

Question 57

What is an insulator?

Answer 57

A thermal insulator acts as a barrier to the transfer of energy by heating.
An electrical insulator doesn’t conduct electricity. E.g acetate and polythene.

Question 58

How can you transfer electrons between an acetate and polythene rod using a duster?

Answer 58

When you rub an acetate rod with a dry duster some of the elections move from the rod to the duster giving the rod a positive charge and the duster a negative charge. When you rub the duster on the polythene rod electrons move from the duster onto the rod and the opposite situation occurs.

Question 59

What is meant by charging by induction?

Answer 59

This is when an object is charged by bringing another charged object near it.

Question 60

Give an example of how an induced charge works using a wall as a balloon:

Answer 60

A charged object can affect the distribution of of charges on an uncharged object. E.g:
If a negatively charged balloon is brought near a wall, the negatively charged electrons in the wall and repelled. This causes the surface of the wall to become positively charged. No catheter are transferred from the balloon so we say the positive charge in the all has been induced. This is called charging by induction.

Question 61

What is a force field?

Answer 61

The volume of space around an object in which another object can experience a force. A magnet has a force field around it called a magnetic field.

Question 62

What is an electric field/electrostatic field?

Answer 62

The force field around a charged object in which it can affect another charged object.