Topic 10

Question 1

What is current ?

Answer 1

Electrical current is the flow (movement) of electric charges

Question 2

What is electrical current measured in ?

Answer 2

Electric current is measured in amperes (A). Current has the same value at any point in a single closed loop

Question 3

How do you calculate the flow of charge ?

Answer 3

The flow of charge (C) = current (A) x time (s).

Question 4

In a closed loop if the current is 10(A) in one point what is it at another point?

Answer 4

10(A)

Because A current has the same value at every point in a single closed loop.

Question 5

I = Q/t

Answer 5

Current (C) = charge(A) / time (s)

Coulombs Amps Seconds

Question 6

current = charge / time

How would you rearrange this equation if you wanted to calculate charge ?

Answer 6

Charge = current x time

Question 7

What are the units for current?

Answer 7

Amperes

Question 8

What is an electrical conductor ?

Answer 8

An electrical conductor is material that allows electric currents (flow of electric charges) to pass through it.

Question 9

What are all electrical conductors made from ?

Answer 9

All metals are electrical conductors

Question 10

What are electrical insulators ?

Answer 10

An electrical insulator is a material that doesn’t allow electric currents (flow of electric charges) to pass through it.

Question 11

What are two electrical insulators ?

Answer 11

Plastic and glass are electrical insulators

Question 12

What allow electrical conductors too conduct electricity?

Answer 12

The free electrons inside electrical conductors explain why they can conduct electricity

Question 13

What makes an electrical insulator ?

Answer 13

An electrical insulator has no free electrons.

No charges are free to move and carry a current.

Question 14

What makes an electrical conductor ?

Answer 14

An electrical conductor has lots of charges that are free to move.

In a metal, the charges that are free to move are electrons.

The electric current through the metal is the flow of these free electrons

Question 15

What is potential difference ?

Answer 15

Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.

Question 16

How can potential difference be described ?

Answer 16

It can be described as the energy transferred by unit charge passed

Question 17

What is potential difference measured in ?

Answer 17

Potential difference (p.d.) is measured in volts (V) and is also called voltage.
The energy is transferred to the electrical components in a circuit when the charge carriers pass through them.

Question 18

What do we use to measure potential difference ?

Answer 18

We use a voltmeter to measure potential difference (or voltage).

Question 19

V =?

Answer 19

E / Q

Question 20

Voltage x charge = ?

Answer 20

Voltage x charge = energy

Question 21

What do ammeters measure ?

Answer 21

An ammeter measures the flow of current that passes through a wire

Question 22

How do ammeters have to be connected ?

Answer 22

Ammeters have to be connected in series (in the same loop of the circuit) with the electrical component whose current you are measuring.

Question 23

What do voltmeters measure ?

Answer 23

Voltmeters measure potential difference (voltage) between two points in a circuit.

For example between two points either side of a component.

Question 24

How do voltmeters have to be connected ?

Answer 24

Voltmeters must always be connected in parallel (on a separate branch of the circuit) with the two points being measured.

Question 25

What’s the difference between current and potential difference ?

Answer 25

The current is a flow of charge. Current is measured through a component. Potential difference is the energy used between two points in a circuit, therefore it is measured between two points either side of a component. We describe this as the potential difference measured across a component.

Question 26

If voltage is 5V and charge is 3C, what is the energy transferred?

Answer 26

Voltage = energy / charge Energy = voltage x charge 5V x 3C = 15J

Question 27

Fact

Answer 27

A potential difference of one Volt is equal to one Joule of energy being used by one Coulomb of charge when it flows between two points in a circuit

Question 28

What is resistance a measure of ?

Answer 28

Resistance is a measure of how difficult it is for current to flow through a component

Question 29

How is resistance measured ?

Answer 29

Resistance is measured in ohms, Ω.

Question 30

When charge flow is in an electrical current the size of the current is affected by what two things?

Answer 30

The resistance: If the resistance is increased, the current will decrease. The potential difference: If the potential difference is increased the current will increase.

Question 31

What is ohm’s law ?

Answer 31

The resistance between two points in a circuit is equal to the potential difference between those two points, divided by the current flowing through them.

Question 32

What’s the symbol and word equation for ohms law ?

Answer 32

``` R = V/I Resistance = potential difference/current ```

Question 33

How would Ohm's Law be rearranged to calculate potential difference .

Answer 33

Potential difference = current x resistance

Question 34

What instruments do we use to calculate resistance ?

Answer 34

We calculate potential difference using a voltmeter and current using an ammeter at the same time

Question 35

When a wire is longer what does this do to the resistance?

Answer 35

The longer the wire, the higher the resistance

Question 36

What do we use to measure a current flowing through a component ?

Answer 36

Ammeter

Question 37

To measure the resistance of a component (e.g. lamp or resistor) what should we do ?

Answer 37

measure the potential difference across the component.

Question 38

What is An Ohmic conductor ?

Answer 38

a conductor that obeys Ohm’s Law.

Question 39

If The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. What does this mean for the resistance?

Answer 39

This means that the resistance remains constant as the current changes.

Question 40

To measure resistance what do you need ?

Answer 40

A voltmeter in parallel An ammeter in series Ohms law