Topic 2 - Controlling and Using Electric Current

Question 1

What is current?

Answer 1

Rate of flow of charge around a circuit

Question 2

What does there need to be in a circuit in order for a current to flow?

Answer 2

A voltage across the circuit

Question 3

What is the unit to measure current?

Answer 3

Ampere, A

Question 4

What is voltage?

Answer 4

Potential difference, driving force that pushes current around, like electrical pressure

Question 5

What is the unit to measure voltage?

Answer 5

Volt, V

Question 6

What is resistance?

Answer 6

Anything in the circuit which slows the flow down

Question 7

What is resistance measured in?

Answer 7

Ohm, Ω

Question 8

What happens to current if you increase the voltage?

Answer 8

More current will flow

Question 9

What happens to current if you increase the resistance?

Answer 9

Less current will flow

Question 10

Potential difference is ______ transferred per ____ ______.

Answer 10

Potential difference is energy transferred per unit charge

Question 11

In a circuit, where is the energy supplied to the charge and how does this affect the voltage?

Answer 11

• Power source

- Increases it

Question 12

What causes charge to decrease in a circuit?

Answer 12

When voltage decreases my components in the circuit e.g. resistors

Question 13

If the change in voltage is bigger, how does this affect the amount of energy transferred for a given charge passing through the circuit?

Answer 13

More energy

Question 14

What is 1 volt in joules/coulombs?

Answer 14

1

Question 15

How does current change around a circuit?

Answer 15

It doesn’t, current is conserved; the total current entering a junction id = to total current leaving a junction

Question 16

What does an ammeter measure?

Answer 16

The current flowing through the component in amps

Question 17

How should an ammeter be put into the circuit?

Answer 17

In series

Question 18

What does a voltmeter measure?

Answer 18

Voltage/potential difference across the component in volts

Question 19

How should a voltmeter be placed in a circuit?

Answer 19

In parallel around the component under test

Question 20

What is the effect of a variable resistor on the current?

Answer 20

Alters the current flowing through the circuit which can be recorded by ammeter/voltmeter, plot on voltage-current graphs

Question 21

How does a diode affect current?

Answer 21

Current only flows through a diode in one direction

Question 22

How does a filament lamp affect current?

Answer 22

As temp increases, resistance increases

Question 23

What si the relation between current through a resistor and voltage?

Answer 23

Propotional

Question 24

What is the equation linking voltage, current and resistance?

Answer 24

Potential difference = current x resistance

Question 25

How does an LDR affect resistance?

Answer 25

- Light dependent resistor - Amount of resistance depends on how light it is - In bright light, resistance falls - In darkness, resistance higher

Question 26

How does a thermistor affect resistance?

Answer 26

- Temperature dependent resistor - Hot: resistance drops - Cold: resistance increases

Question 27

Why do resistors get hot when an electric current passes through them?

Answer 27

- Energy transfer heats resistor - Energy transfer due to electrons colliding w/ ions in lattice that make up resistor as move through it - Collisions give ions in lattice extra energy emitted as heat increasing resistor's resistance reducing curent flow (or more voltage for same current); if too hot, no current flows - Heating causes circuits to be less efficient as energy wasted. Can cause components to melt (circuit stops working) - Fuses use this effect to protect circuits: melt + break circuit if current gets too high

Question 28

What are the advantages of the heating effect in a resistor?

Answer 28

- Good if you want to heat something - e.g. toasters - Current passes through coil, temp. increases so much so it glows + gives off infrared (heat) radiation that cooks bread - Light bulbs work in similar way

Question 29

How does an appliance with a high power rating transfer energy?

Answer 29

Transfers lots of energy in a short time

Question 30

What is power measured in?

Answer 30

Watts, W

Question 31

What is the equation linking electrical power potential difference and current?

Answer 31

Electrical power = potential difference x current

Question 32

What is the equation linking energy transferred, current, potential difference and time?

Answer 32

Energy transferred = current x potential difference x time