Section 6 Electricity

Question 1

What is current

Answer 1

The rate of flow of charge

Question 2

What is a coulomb

Answer 2

The amount of charge that passes in 1 second when the current is one ampere

Question 3

What is the equation to find coulombs, when using current and time

Answer 3

Charge in coulombs =current × time taken
(Change in) Q = I × (change in) t
Coulombs = current × time taken

Question 4

What is used to measure current in a circuit

Answer 4

An ammeter (set up in series)

Question 5

What is potential difference

Answer 5

Work done in moving a unit charge between the points

Question 6

What equation is used to find potential difference when given work done and charge

Answer 6

V = W ÷ Q
Pd = work done ÷ charge
Volts = joules ÷ coulombs

Question 7

What is used to measure potential difference in a circuit

Answer 7

A voltmeter (must be parallel to the component)

Question 8

What is resistance

Answer 8

A measure of how difficult it is to get a current to flow

Question 9

What equation is used for finding resistance, when given potential difference and current

Answer 9

R = V ÷ I
Resistance = potential difference ÷ current
Ohms = volts ÷ amps

Question 10

What is ohms law

Answer 10

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

Question 11

What does it mean if the gradient is shallower on an I-V graph

Answer 11

The component has a higher resistance

Question 12

What does an I-V graph of an ohmic conductor look like

Answer 12

A positive straight line directly proportional

Question 13

What does an I-V graph of a filament lamp look like

Answer 13

A curve that starts steep but gets shallower as the voltage rises

Question 14

What does an I-V graphics diode look like

Answer 14

An exponential graph from the origin ( must have a threshold voltage (forward bias))

Question 15

What is resistivity

Answer 15

How much a particular material resists current flow ( including the structure of the material and environmental factors)

Question 16

What is the equation for resistivity when given resistance cross sectional area and length

Answer 16

Rho = ( R×A ) ÷ L
Resistivity = (resistance×cross sectional area) ÷ length
Ohmic meters = (ohms×metres(2))÷ metres

Question 17

What are semiconductors

Answer 17

A group of materials that aren’t as good at conducting electricity as metals

Question 18

What is a thermistor

Answer 18

A component with a resistance that depends on it’s temperature

Question 19

What is special about ntc thermistors ( negative temperature coefficient)

Answer 19

Resistance decreases as the temperature goes up

Question 20

What is a superconductor

Answer 20

When a material cools below their critical temperature, their resistivity disappears entirely. Without resistance none of the electrical energy is turned into heat.

Question 21

What are the uses for superconductors (3)

Answer 21

Power cables that transmit energy without the loss of power
Really strong electromagnets ( medicine and make trains)
Electronic circuits that work really fast with minimal energy loss

Question 22

What is power?

Answer 22

The rate of energy transfer and measured in watts (where 1 watt is equivalent to 1 joule per second)

Question 23

What is the equation for power when given pd and current

Answer 23

P = I × V
Power = current × pd
Watts = amps × volts

Question 24

What is the equation for power when given voltage and resistance

Answer 24

P = V(squared) ÷ R
Power = voltage ( squared) ÷ resistance
Watts = volts(squared) ÷ ohms

Question 25

What is the equation for power when given current and resistance

Answer 25

P = I(squared) × R
Power = current (squared) × resistance
Watts = amps (squared) × resistance

Question 26

How can you figure out energy

Answer 26

By substituting P = E ÷ t into the power equations dependant on the variable given.

Question 27

What are the rules for voltage when in a series curcuit

Answer 27

V(total) = v1+ V2 + V3 …

Question 28

What the rules for resistance when in series

Answer 28

R(total) = r1 + r2 + r3…

Question 29

What are the rules for current when in parallel

Answer 29

Current is split at each junction so:
I = i1 + i2 + i3 … ( At each junction explicitly
Splits as a ratio comparatively to each component on each branch

Question 30

What are the rules for resistance when in parrallel

Answer 30

1/R(total) = 1/R1 + 1/R2 + 1/R3 …

Question 31

What are the rules for current when in series

Answer 31

Stays the same throughout

Question 32

What are the rules for voltage when in a parallel circuit

Answer 32

Stays the same throughout