Electricity

Question 0

What is the equation to calculate the total number of electrons that have flowed in a current?

Answer 0

N = Q/e

Question 1

What is the equation for calculating charge?

Answer 1

Q = I x T

Question 2

Define mean drift velocity

Answer 2

The average velocity that charge carriers (electrons) move down the wire.

Question 3

What are the components of I = AneV?

Answer 3

I = current
A = cross sectional area of conductor
n = number of free electrons per m^3
e = 1.6 x 10^-19
V = drift velocity

Question 4

Define emf

Answer 4

Emf is the energy transferred by the supply, per unit charge from other forms, to electrical

Question 5

Define potential difference

Answer 5

P.d. Is the energy transferred per coulomb of charge from electrical energy to other forms

Question 6

What is a volt?

Answer 6

1 volt = 1J/C

Question 7

What is the equation for calculating voltage, when given energy transferred and charge?
In Joules and coulombs

Answer 7

P.d. (V) = Energy transferred (W for work done) / Charge (C)

Question 8

Define resistance

Answer 8

Resistance is a measure of the opposition a material exerts against the flow of electrons

Question 9

What causes resistance?

Answer 9

The metal ions interfere with the motion of the electrons, causing resistance.

Question 10

What is ohms law?

Answer 10

Current in an oh mic conductor is proportional to the voltage across it.

Provided that temperature and other physical conditions are constant.

Question 11

What is kirchoff’s first law

Answer 11

Sum of the current in = the sum of the currents out, at any junction

Question 12

What is kirchoff’s second law

Answer 12

Sum of the EMFs = sum of the PDs, around any closed loop

Question 13

What is the equation to calculate resistivity

Answer 13

Resistance = (resistivity x length) / area
R = pl/a

Question 14

What is the unit of resistivity?

Answer 14

The ohm meter

Question 15

What is the equation linking power, energy and time?

Answer 15

Power = energy / time

Question 16

What is the derived equation linking power, current and resistance?

Answer 16

P = I^2 x R

Question 17

Define a kilowatt hour

Answer 17

It is the amount of energy transferred by a 1KW device in an hour

1KW = 3.6MJ

Question 18

What is the definition of a coulomb?

Answer 18

A coulomb is the amount of charge that passes a point in a circuit when a current of 1 amp flows for 1 second.

Question 19

What is an ohm?

Answer 19

1 ohm is the resistance when the ratio of p.d. across a component to current through it is 1 volt per amp

Question 20

What is power?

Answer 20

Power is the rare at which energy is transferred (or work is done)

1 watt is 1 joule per second

Question 21

What is the equation that calculates EMF using current and 2 different resistances?

Answer 21

EMF = i(R + r)

EMF = current x (Resistance of circuit + internal resistance of supply)

Question 22

What is the equation relating voltage, work done and charge?

Answer 22

Voltage = work done (J) / Q (C)

Question 23

What is the equation that relates energy, power and time?

Answer 23

Energy (J) = power (W) x time (s)

Question 24

V = emf - Ir

Answer 24

V = emf - Ir