Electricity

Question 1

What is current?

Answer 1

rate of flow of charge

Question 2

What is a coulomb?

Answer 2

the amount of charge passing a point per second when the current is 1A

Question 3

What is ohms law?

Answer 3

provided all physical conditions are constant, Voltage is proportional to current (lower gradient = lower R)

Question 4

What is potential difference?

Answer 4

The work done transferring a unit of charge between 2 points

Question 5

Why does the gradient of a filament lamp curve get shallower as voltage increases?

Answer 5

Increased voltage causes current to increase. The increased current results in a heating effect, this therefore causes resistance to increase.

Question 6

What is an ohm?

Answer 6

An ohm is the resistance of a circuit when a potential difference of 1 V causes a current of 1 A to flow?

Question 7

What is resistivity?

Answer 7

Resistivity is a measure of how much a particular metal resists current flow

Question 8

What does a bigger area mean?

Answer 8

more electrons flow (learn what is proportional to what)

Question 9

resistivity and conduction

Answer 9

smaller resistivity = better conductor (inversely proportional)

Question 10

What is power?

Answer 10

rate of energy transfer (1 W = 1 J/s)

Question 11

What is an ideal voltmeter?

Answer 11

An ideal voltmeter has infinite resistance so no current can flow through them

Question 12

What is an ideal ammeter?

Answer 12

An ideal ammeter has 0 resistance so there is no potential difference across them

Question 13

Why are semi conductors good sensors?

Answer 13

semi conductors are poor conductors as they have fewer electrons. However, when energy is supplied to them they release a lot more electrons and their resistivity drops (making them good sensors)

Question 14

What happens to resistance of thermistors/ LDRs?

Answer 14

Thermistor temp up = resistance down

LDR light up = resistance down

Question 15

What is a superconductor?

Answer 15

A superconductor is a material whose resistivity drops to 0 below a critical temperature

Question 16

What are superconductors used for?

Answer 16

Strong electromagnets, power cables (low power loss), fast circuits (low energy loss)

Question 17

What is emf?

Answer 17

Emf is the amount of energy a battery produces and transfers per coulomb of charge

Question 18

What causes lost volts?

Answer 18

internal resistance of a battery

Question 19

potential divider equations?

Answer 19

Vout = (R2/R1+R2)xVs
I = Vs/R1+R2 = Vout/R2

Question 20

Pd and current in series?

Answer 20

Pd splits in series but current is the same

Question 21

Pd and current in parallel?

Answer 21

Pd the same in parallel but current splits

Question 22

diodes?

Answer 22

Diodes are components that only let current flow at a threshold voltage (0.6v) and only let current flow in the forward bias direction (v high resistance in reverse bias)

Question 23

cells in series?

Answer 23

E total = E1 + E2 ….. ( current gains a bit of emf from each cell)

Question 24

Cells in parallel?

Answer 24

E total = E of individual cells ( current gains all emf from individual cell)

Question 25

What is a diodes threshold voltage?

Answer 25

It is the voltage at which the diode has enough power to conduct a large amount of current

Question 26

Why are potentiometers better than voltmeters?

Answer 26

They give the exact value for voltage as they don’t draw any current away from the circuit (ideal voltmeter)

Question 27

What do potentiometers allow you to do?

Answer 27

Allow you to vary R1 and R2 and so you can vary Vout

Question 28

What can potentiometers be used for?

Answer 28

They allow you to vary the voltage continuously (volume speaker)