2.1 - Electricity (Current, Potential Difference and Resistance)

Question 1

What is required for electrical charge to flow through a closed circuit?

Answer 1

The circuit must include a source of potential difference.

Question 2

What is electric current?

Answer 2

Electric current is a flow of electrical charge.

Question 3

What does the size of an electric current mean?

Answer 3

The rate of flow of electrical charge (how fast the charge is flowing)

Question 4

How are Charge flow, current and time linked?

Answer 4

Charge Flow = current × time

[Q = I × t]

Question 5

What is the unit for Charge?

Answer 5

Coulomb ( C )

Question 6

What symbol is normally used to represent charge in equations?

Answer 6

Q

Question 7

What is the unit of current

Answer 7

Amperes ( A )

Question 8

What is the symbol normally used to represent current in equations?

Answer 8

I

Question 9

How does current change around a closed loop?

Answer 9

It doesn’t: a current has the same value at any point in a single closed loop.

Question 10

What is the symbol for an open switch?

Answer 10

[TBC]

Question 11

What is the symbol for a closed switch?

Answer 11

[TBC]

Question 12

What is the symbol for a lamp?

Answer 12

[TBC]

Question 13

What is the symbol for a fuse?

Answer 13

[TBC]

Question 14

What is the symbol for a cell?

Answer 14

[TBC]

Question 15

What is the symbol for a voltmeter?

Answer 15

[TBC]

Question 16

What is the symbol for a battery?

Answer 16

[TBC]

Question 17

What is the symbol for an ammeter?

Answer 17

[TBC]

Question 18

What is the symbol for a diode?

Answer 18

[TBC]

Question 19

What is the symbol for a thermistor?

Answer 19

[TBC]

Question 20

What is the symbol for a resistor?

Answer 20

[TBC]

Question 21

What is the symbol for a variable resistor?

Answer 21

[TBC]

Question 22

What is the symbol for an LDR?

Answer 22

[TBC]

Question 23

What is the symbol for an LED?

Answer 23

[TBC]

Question 24

What two properties of a component affect the current passing through it?

Answer 24

Resistance of the component and potential difference across it

Question 25

How are current, resistance and potential difference related for a component?

Answer 25

potential difference = current × resistance [V = I R]

Question 26

What is the unit of potential difference?

Answer 26

Volts ( V )

Question 27

What is the symbol normally used to represent potential difference in equations?

Answer 27

V

Question 28

What is the unit of resistance?

Answer 28

Ohms ( Ω )

Question 29

What is the symbol normally used to represent resistance in equations?

Answer 29

R

Question 30

In what conditions the current passing through a component *directly proportional* to the potential difference across it?

Answer 30

* If the component is ohmic * If the component is at constant temperature

Question 31

What is an ohmic conductor

Answer 31

A component for which the resistance stays constant for a given current and potential difference. (A component that obeys Ohm's law [V = IR])

Question 32

How are current and potential difference related for ohmic components?

Answer 32

Resistance is constant, so current is directly proportional to potential difference (V = IR) [Graph TBC]

Question 33

Do all components have a fixed resistance?

Answer 33

No, the resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.

Question 34

How does the potential difference of a filament lamp change as current increases

Answer 34

* Current increase leads to temperature increase (light turns on) * Temperature increase leads to resistance increase * Resistance increase leads to potential difference decrease (V = IR) [Graph TBC]

Question 35

How does the potential difference of a diode change as current varies?

Answer 35

* Diode only let current flow in one direction * When current is negative, resistance is very high * Very high resistance, so potential difference is very low (V=IR) * When current is positive, resistance is very low * Very low resistance, so potential difference is very high (V=IR) [Graph TBC]

Question 36

What is a thermistor?

Answer 36

A component where the resistance *decreases* as the temperature increases

Question 37

What might a thermistor be useful for?

Answer 37

Electrical circuits which need to vary based on temperature (e.g. a thermostat)

Question 38

What is an LDR

Answer 38

Light Dependent Resistor Resistance *decreases* as light intensity increases

Question 39

What might an LDR be useful for?

Answer 39

Electrical circuits which need to vary based on light (e.g. streetlamps which turn on when it gets dark)

Question 40

How can you measure the resistance of a component?

Answer 40

* Create a circuit with the component * unbroken circuit * has a power source * Measure the current passing through the component * Ammeter * In series (because current is constant in a single loop) * Measure the potential difference passing through the component * Voltmeter * In parallel with the component (measuring the difference between *before* and *after* the component) * Resistance is the potential difference divided by the current (V = I R )