Electricity

Question 1

What is electricity?

Answer 1

Electricity is a flow of charge or charges like electrons.

Question 2

What do electrons carry?

Answer 2

Electrons carry energy from a source of energy to a component.

Question 3

What is the difference between cells and batteries?

Answer 3

Cells and batteries are essentially the same thing and perform the same job.

Question 4

What is a battery’s function?

Answer 4

A battery has a store of chemical potential energy.

Question 5

What happens when a battery is connected in a complete circuit?

Answer 5

The chemical potential energy is transferred to the electrons which move through the wires.

Question 6

What is current?

Answer 6

Current is the movement of charge, and it always goes from the positive terminal of the battery to the negative.

Question 7

What happens to electrons as they pass through a bulb?

Answer 7

Their energy is converted into light, but the electrons do not disappear.

Question 8

What keeps the light bulb on?

Answer 8

The constant flow of electrons transferring energy keeps the light bulb on.

Question 9

What do we measure potential difference (PD) with?

Answer 9

We measure PD with a voltmeter.

Question 10

How is PD measured?

Answer 10

Voltmeter leads are connected in parallel to the components you want to measure the voltage of.

Question 11

What does a voltmeter measure across a battery?

Answer 11

It should measure the voltage supplied to the electrons in the circuit.

Question 12

What is the equation for potential difference (PD)?

Answer 12

PD in volts is equal to energy in joules divided by charge in coulombs.

Question 13

What is the formula for current?

Answer 13

Current in amps equals charge in coulombs divided by time in seconds.

Question 14

What is the symbol for current?

Answer 14

The symbol for current is capital I.

Question 15

How is current measured?

Answer 15

Current is measured with an ammeter.

Question 16

What is resistance?

Answer 16

Resistance is the opposition to the flow of charge or current through components.

Question 17

What happens to current when PD increases in a resistor?

Answer 17

An increasing PD results in a greater current flowing.

Question 18

What does Ohm’s law state?

Answer 18

Ohm’s law states that V equals IR.

Question 19

How can resistance be calculated from an IV graph?

Answer 19

Resistance can be calculated by picking a point on the line and rearranging Ohm’s law.

Question 20

What is a diode?

Answer 20

A diode only lets current flow through in one direction.

Question 21

What is a superconductor?

Answer 21

A superconductor is a material that has a resistance of zero.

Question 22

What is resistivity?

Answer 22

Resistivity is the resistance of a cube of unit length sides of that material.

Question 23

What is the equation for resistivity?

Answer 23

R equals rho l over a, where rho is resistivity in ohm meters.

Question 24

What happens to current and PD in series circuits?

Answer 24

Total PD is shared, current is the same for all, and total resistance is the sum of all resistances.

Question 25

What happens to current and PD in parallel circuits?

Answer 25

The PD is the same for every branch, current is shared, and total resistance decreases.

Question 26

What is a thermistor?

Answer 26

A thermistor's resistance decreases if the temperature increases.

Question 27

What is an LDR?

Answer 27

An LDR is a light dependent resistor whose resistance goes down with increased light intensity.

Question 28

What is power in terms of electricity?

Answer 28

Power is the rate of energy transferred, calculated as energy divided by time.

Question 29

What is the equation for power in electricity?

Answer 29

P equals Vi, where P is power, V is voltage, and i is current.

Question 30

What does light intensity affect in a circuit with an LDR?

Answer 30

As light intensity goes down, the resistance of the LDR goes up, increasing its share of the voltage.

Question 31

What is power in terms of energy?

Answer 31

Power is the rate of energy transferred, calculated as energy divided by time.

Question 32

How can power also be calculated in electrical terms?

Answer 32

Power (P) can be calculated using the equation P = Vi, where V is voltage and i is current.

Question 33

What type of current does a battery produce?

Answer 33

A battery produces direct current (DC).

Question 34

What is the difference between AC and DC?

Answer 34

AC (alternating current) is needed to transmit electricity over long distances, while DC (direct current) flows in one direction.

Question 35

What is the peak voltage of the live wire in mains electricity?

Answer 35

The live wire varies between plus 325 volts and minus 325 volts, making the peak voltage 325 volts.

Question 36

How is RMS voltage calculated from peak voltage?

Answer 36

To convert from peak voltage to RMS voltage, divide the peak voltage by root 2.

Question 37

What is the UK mains voltage in RMS?

Answer 37

The UK mains voltage is known to be 230 volts, which is the RMS value.

Question 38

How is average power related to peak power?

Answer 38

Average power is half the peak power delivered.

Question 39

What is terminal PD?

Answer 39

Terminal PD is the voltage available to the rest of the circuit, which can be less than the EMF due to internal resistance.

Question 40

What is the equation for EMF?

Answer 40

EMF (ε) equals terminal PD (V) plus I times little r, where little r is internal resistance.

Question 41

What happens to terminal PD as load resistance increases?

Answer 41

As load resistance increases, the current decreases, resulting in less PD being lost in the battery, thus increasing terminal PD.

Question 42

What does the gradient of the terminal PD vs. current graph represent?

Answer 42

The magnitude of the gradient is equal to the internal resistance of the battery.

Question 43

What does the y-intercept of the terminal PD vs. current graph represent?

Answer 43

The y-intercept is equal to the EMF, indicating that with no current flowing, the circuit should receive the full EMF.