Electricity

Question 1

define current and give a matching equation

Answer 1

The rate of flow of charge I = Q/t

Question 2

Define voltage and give a matching equation

Answer 2

work done per unit charge V=W/Q

Question 3

Define Electromotive force and provide a matching equation

Answer 3

work done by a voltage source per unit charge

emf = E/Q

Question 4

give two equations for energy in terms of V

Answer 4

E= VQ

E=VIt

Question 5

Give three equations for power

Answer 5

P = VI = I²R= V²/R

Question 6

Give an equation for resistivity

Answer 6

ρ= RA/L

Question 7

describe an equation to find resistivity

Answer 7

1. measure the diameter of the wire, and find the cross sectional area
2. set up s circuit with a voltmeter in parallel to the wire and an ammeter in series. have a ruler on the wire and crocodile clips determining its length
3. measure V and I for different values of L
4. use R=V/I to find resistance
5. plot R against L and the gradient will be ρ/A

Question 8

state ohm’s law.

Answer 8

in an ohmic conductor current is directly proportional to voltage at a constant temperature

Question 9

describe superconductors

Answer 9

a superconductor has 0 resistance below their critical temperature.
they can be used in strong magnets and power transmission

Question 10

In an LDR, describe the trend between light intensity and resistance

Answer 10

resistance decreases as light intensity increases

Question 11

describe an I-V graph for an ohmic conductor

Answer 11

a straight line graph, that intersects the origin

Question 12

describe an I-V graph for a diode

Answer 12

an exponential graph upwards in the positive quarter that goes through the origin

Question 13

state Kirchhoff’s laws

Answer 13

total current into a junction = total current out

total emf around a loop = total potential difference dropped across the components

Question 14

describe voltage across components of a parallel circuits

Answer 14

the voltage dropped across components in parallel is the same

Question 15

describe a potential divider.

Answer 15

a group of resistors in series across a voltage source, that splits voltage between resistors in direct proportion to their resistance

Question 16

explain internal resistance

Answer 16

the resistance of the materials across a battery or cell, across which some voltage is dropped

Question 17

what is terminal potential difference?

Answer 17

the potential difference across the terminals of a power source, which is equal to the pd across the load