Electricity

Question 1

Define current

Answer 1

The rate of flow of charge

Question 2

Define Potential Difference

Answer 2

The work done per unit charge

Question 3

What does Ohm’s Law State

Answer 3

Provided physical conditions remain constant, the current through an ohmic conductor is directly proportional to the potential difference across it

Question 4

Ohms Law states that physical conditions must stay constant, what are some of these physical conditions

Answer 4

• Temperature
• Pressure
• Light Level

Question 5

What does an ideal ammeter mean

Answer 5

Having no resistance

Question 6

What does an ideal voltmeter mean

Answer 6

Having infinite resistance

Question 7

For an ohmic conductor describe the Current vs Voltage Graph

Answer 7

A straight line passing through the origin

-Constant gradient, as R is constant

Question 8

I-V Characteristics of a semi-conducting diode

Answer 8

• Not as good at conducting as metals, as there are fewer charge carriers
• But if energy is supplied to the semiconductor more charge carriers are released

Question 9

I-V Characteristics of a filament lamp

Answer 9

• Non-ohmic component
• Produce a curve on an I-V graph, passing through the origin
• The curve starts steep but gets shallower as voltage rises

Question 10

Why does a filament lamp not produce a straight line I-V graph

Answer 10

• Because its resistance isn’t constant
• As the current increases the temperature of the wire inside the lamp increases
• As temperature increases resistance increase, as higher temperatures cause the atoms in the wire to vibrate more, leading to more collisions between the electrons and the atoms

Question 11

Characteristic of a negative temperature coefficient thermistor

Answer 11

As temperature increases, resistance decreases. Because as temperature increase more electrons have enough energy to escape from their atoms, meaning there are more charge carriers available

Question 12

define resistivity

Answer 12

the resistivity of a material is defined as the resistance of a 1m length with a 1m^2 cross sectional area. Measured in ohm-metres

Question 13

What does resistivity depend on

Answer 13

• Length of wire- the longer the wire the more difficult it is for current to flow
• Cross Sectional area of wire- the wider the wire the easier it is for electrons to flow
• Resistance of a material

Question 14

Describe the effect of temperature on the resistance of metal conductors.

Answer 14

As temperature increases resistance increase becauseatoms in the maerial have more energy and therefore vibrate more leading to a higher number of collisions

Question 15

Applications of thermistors

Answer 15

Temperature Sensors

Question 16

Define Superconductivity

Answer 16

Superconductivity as a property of certain materials which have zero resistivity at or below the critical temperature.

Question 17

Use of Superconductors

Answer 17

• Produce strong electromagnetics that don’t need a constant power source, used in medical applications
• In power cables, to reduce energy losses in the transmission of electrical power

Question 18

What is the issue with superconductors

Answer 18

That the critical temperature is generally around -263 degrees celcius

Question 19

How can a potential divider provide a constant or variable potential difference from a power supply.

Answer 19

• You can use a potential divider to supply a potential difference to the circuit between zero and the potential difference across the voltage source as you can vary the resistance of the circuit

Question 20

Define EMF

Answer 20

Energy provided by a cell per coulomb of charge passing through it

Question 21

Define Terminal pd

Answer 21

The energy transferred per coulomb of charge to the components

Question 22

State Kirchoffs first law

Answer 22

the sum of the currents arriving at the junction = the sum of the currents leaving the junction.

Question 23

State Kirchoffs second law

Answer 23

energy supplied by a power supply is equal to the sum of the energies of power dissipation in a circuit’

Question 24

2 ways of measuring emf and internal resistance

Answer 24

• The emf is equal to the potential difference across the terminals of a battery. If you connect a voltmeter across the terminals you will get a value very close to the emf as little current will low
• If you vary the current and measure the pd, then plot a graph of V against I then the gradient is equal to the internal resistance and the y-intercept is equal to the emf

Question 25

2 ways of measuring emf and internal resistance

Answer 25

• The emf is equal to the potential difference across the terminals of a battery. If you connect a voltmeter across the terminals you will get a value very close to the emf as little current will low
• If you vary the current and measure the pd, then plot a graph of V against I then the gradient is equal to the internal resistance and the y-intercept is equal to the emf

Question 26

Advantages of a low internal resistance

Answer 26

• Internal resistance limits current hence can provide a higher current
• Energy wasted in battery is lower
• A battery charges quicker as current is higher
• Higher terminal voltage as less lost volts

Question 27

Characteristics of diodes

Answer 27

• Only let current flow in one direction
• Forward bias= direction current is allowed to flow in
• Have a threshold voltage of around 0.6v in the forward direction before they will conduct
• In reverse bias the resistance of the diode is very high and the current that flows is very tiny