Topic 5 -Electricity and Circuits

Question 1

What is current?

Answer 1

The flow of electric charge - the rate of flow of charge

Question 2

When is the only time a current will flow through an electrical component?

Answer 2

If there is a potential difference across the component and if the circuit is complete

Question 3

What is the unit for current?

Answer 3

Ampere (A)

Question 4

What is potential difference?

Answer 4

• The same as voltage
• the driving force that pushes the charge around the circuit
• the energy transferred per coulomb of charge that passes between two points in an electrical circuitry

Question 5

What is the unit for voltage/potential difference?

Answer 5

Volt (V)

Question 6

What is resistance?

Answer 6

Anything that slows the flow of the charge down

Question 7

What is the unit for resistance?

Answer 7

Ohms (Ω)

Question 8

How does the potential difference affect the current?

Answer 8

The higher the potential difference across a given component, the higher the current will be

Question 9

How does resistance affect the current?

Answer 9

The greater the resistance of a component, the smaller the current

Question 10

In metals what is current caused by?

Answer 10

The flow of electrons

Question 11

What is the symbol for current?

Answer 11

I

Question 12

What is the equation relating charge, current and time?

Answer 12

Charge = current x time

Q

I t

Question 13

When does more charge pass around a circuit in a given time?

Answer 13

When a greater current flows

Question 14

What is charge measured in?

Answer 14

Coulombs (C)

Question 15

SYMBOL CARDS USING WEBSITE

Answer 15

SYMBOL CARDS USING WEBSITE

Question 16

How can you calculate energy transferred from charge and potential difference?

Answer 16

Energy transferred = charge moved x potential difference

E = Q x V

Question 17

What is energy measured in?

Answer 17

Joules

Question 18

What is the potential difference across an electrical component?

Answer 18

The amount of energy transferred by that electrical component per unit of charge passed

Question 19

What is one volt equal to?

Answer 19

One joule per coulomb

Question 20

How can you calculate voltage from current and resistance?

Answer 20

Potential difference = current x resistance

V = I x R

Question 21

When an electrical charge flows through a component what does it have to do?

Answer 21

Do work against resistance

Question 22

What does work done against resistance cause?

Answer 22

An electrical transfer of energy

Question 23

What is work done equal to?

Answer 23

Energy transferred

Question 24

When a current flows through a resistor what happens? Why?

Answer 24

• The resistor heats up
• Because some of the energy transferred is dissipated to the thermal energy stores of the component and the surroundings - not all of the energy from work done against resistance is transferred usefully

Question 25

How is energy transferred to the thermal energy stores of a component and the surroundings?

Answer 25

The electrons collide with the ions as they flow through the lattice which makes up the resistor.

Question 26

Why does the current decrease as a resistor heats up if there is a given p.d.?

Answer 26

The more the ions vibrate, the more difficult it is for electrons to get through the resistor because there are more collisions

Question 27

What does p.d. stand for?

Answer 27

Potential difference

Question 28

What happens if a resistor gets too hot?

Answer 28

No current will be able to flow (apart from with thermistors)

Question 29

What happens to the resistance or a thermistor with an increase in temperature?

Answer 29

It decreases

Question 30

What do low resistance wires do to the energy dissipated to thermal energy stores when current flows between components?

Answer 30

Decrease the energy dissipated

Question 31

What circuit can you use to investigate the relationship between current, p.d. and resistance for a range of components?

Answer 31

A parallel circuit with a variable d.c. source of power with an ammeter in series and a voltmeter in parallel around any resistor

Question 32

What components can you investigate in a circuit to investigate the relationship between current, p.d. and resistance?

Answer 32

A filament bulb or a fixed resistor

Question 33

What does an ammeter measure?

Answer 33

The current flowing though a component in amps

Question 34

Where should an ammeter be placed in a circuit?

Answer 34

Anywhere in the main circuit but it must be in series, NEVER IN PARALLEL

Question 35

What does a voltmeter measure?

Answer 35

The potential difference across a component

Question 36

Where must a voltmeter be placed in a circuit?

Answer 36

In parallel with the component under test