Electricity

Question 1

What is effective resistance

Answer 1

the measure of the resistance of all the resistors throughout the circuit.

Question 2

Current vs voltage graph for a wire

Answer 2

Question 3

Current vs voltage graph for a lamp

Answer 3

Question 4

Current vs voltage graph for a thermistor

Answer 4

Question 5

Current vs voltage graph for a diode

Answer 5

Question 6

Diode and light emitting diode diagram

Answer 6

Question 7

Resistor, variable resistor, thermistor and light dependant resistor diagrams

Answer 7

Question 8

Heater diagram

Answer 8

Question 9

Electric motor diagram

Answer 9

Question 10

What is an ohmic conductor

Answer 10

A conductor that obeys Ohm’s Law

Question 11

What is a LDR also known as and when is its resistance highest?

Answer 11

Photocell - when the light intensity is lowest

Question 12

Graphs for a capacitor (charge, voltage and current)

Answer 12

Question 13

What is the electromotive force

Answer 13

The potential difference across the terminals of a battery when no current flows

Question 14

What are lost volts

Answer 14

The voltage used to overcome the internal resistance of the battery

Question 15

What is the terminal voltage

Answer 15

The voltage delivered to the load resistance in the circuit (the p.d when no current flows; the terminal voltage is the p.d when current flows)

Question 16

Equation linking charge current and time taken for a capacitor to reach the charge

Answer 16

Q=I x t

Question 17

describe in terms of electron flow what is happening when a capacitor charges up

Answer 17

Capacitors are charged by a power supply (e.g., a battery)
One plate of the capacitor is connected to the positive terminal of the power supply
The positive terminal ‘pulls’ electrons from this plate
Hence the plate nearest the positive terminal becomes positively charged
These electrons travel around the circuit and are pushed from the negative terminal of the power supply
The negative terminal ‘pushes’ electrons onto the other plate
Hence the plate nearest the negative terminal becomes negatively charged
As the negative charge builds up, fewer electrons are pushed onto the plate due to electrostatic repulsion from the electrons already on the plate
When no more electrons can be pushed onto the negative plate, the charging stops

Question 18

How are capacitors used?

Answer 18

Question 19

What is the time constant of capacitance

Answer 19

Time taken for charge or potential difference to increase by 63% OR fall by 37%

Question 20

Capacitance def

Answer 20

Charge stored per unit potential difference

Question 21

Graphical method for measuring time constant of capacitance

Answer 21

Question 22

Mathematical method for calculating the time constant of capacitance

Answer 22

Question 23

Answer 23

Question 24

What is one farad equal to?

Answer 24

1 coulomb per volt (C/V)

Question 25

What is the energy store in a capacitor

Answer 25

- Electric potential energy - it is the energy stored in the electric field formed by the oppositely charged plates

Question 26

Calculating the energy stored in a capacitor graphically

Answer 26

Question 27

Dielectric material def

Answer 27

Question 28

What do the components of this equation mean?

Answer 28

Question 29

What do the components of this equation mean?

Answer 29

Question 30

What happens when a dielectric is placed between the plates of a capacitor?

Answer 30

The individual molecules become polarised

Question 31

Do dielectric materials have different permitivities?

Answer 31

Yes - this is the ability for the dielectric to hold an electrical charge. This is shown by the letter E

Question 32

EMF definition

Answer 32

The amount of chemical energy converted to electrical energy per coulomb of charge (C) when passing through a power supply equal to the terminal potential difference when no current flows.

Question 33

EMF Equation

Answer 33

Question 34

is EMF a force

Answer 34

It is not actually a force, and is measured in volts

Question 35

how is emf measured

Answer 35

Question 36

what is terminal potential difference

Answer 36

the potential difference across the terminals of a cell If there was no internal resistance, the terminal p.d would be equal to the e.m.f Since a cell has internal resistance, the terminal p.d is always lower than the e.m.f

Question 37

describe what lost volts are and why they exist

Answer 37

- In a closed circuit, current flows through a cell and a potential difference develops across the internal resistance - Since resistance opposes current, this reduces the energy per unit charge (voltage) available to the rest of the external circuit - This difference is called the ‘lost volts' - Lost volts is usually represented by little v

Question 38

lost volts def

Answer 38

The work done per unit charge / coulomb to overcome the internal resistance / resistance inside the battery (when current flows)

Question 39

internal resistance def

Answer 39

The resistance of the materials within the battery