9 Energy Power And Resistance

Question 1

Potential difference

Answer 1

A measure of the transfer of energy by charge carriers

Question 2

Volts

Answer 2

The potential difference across a component when 1 J of energy is transferred per unit charge passing through the component

Question 3

W = QV

Answer 3

Work done = charge x potential difference

Question 4

Voltmeter

Answer 4

Measures in parallel and ideally infinite resistance

Question 5

Difference between potential difference and electromotive force

Answer 5

P.d. Describes the work done by the charge carriers
EMF describes the work done on the charge carriers

Question 6

Special E = W / Q

Answer 6

EMF = work done / charge

Question 7

What is an electron gun

Answer 7

A device used to produce a narrow beam of electrons

Question 8

How does an electron gun work

Answer 8

Filament is heated releasing electrons through thermionic emission.
This is done in a vacuum with a large pd over the filament and the anode which has a small gap in it

Question 9

E = VQ

Answer 9

Energy = potential difference x charge

Question 10

eV = 1/2 m v^2

Answer 10

Work done on an electron = gain in kinetic energy

Question 11

V = IR

Answer 11

Potential difference = current x resistance

Question 12

Ohm

Answer 12

The resistance of a component when a p.d. is produced per ampere of current in it

Question 13

Ohms law

Answer 13

The current in a wire is directly proportional to the p.d. across the wire

Question 14

Ohmic conductor

Answer 14

Anything that obeys ohms law

Question 15

Current p.d. graph diode

Answer 15

While p.d. is negative current is 0 while p.d. is small current is also 0 then increases exponentially

Question 16

What effects resistance

Answer 16

Material
Length
Cross sectional area

Question 17

R = (rho L) / A

Answer 17

Resistance = ( resistivity x length ) / cross sectional area

Question 18

Resistance length graph find resistivity

Answer 18

Gradient x cross sectional area

Question 19

What is the rough resistivity of conductors

Answer 19

10^-8

Question 20

What is the rough resistivity of insulators

Answer 20

10^16

Question 21

How does a thermistor work

Answer 21

As temperature increases the number of charge carriers increases and therefore resistance decreases

Question 22

Describe the current p.d. graph for a thermistor

Answer 22

As p.d. become more negative current decreases exponentially and as p.d increases current increases exponentially

Question 23

How does an LDR work

Answer 23

As light intensity increases more charge carriers are released increasing current and decreasing resistance

Question 24

Electrical power

Answer 24

The rate of energy transferred by each electrical component

Question 25

P = IV

Answer 25

Power = current x potential difference

Question 26

W = VIt

Answer 26

Work done = potential difference x current x time

Question 27

P = W/t

Answer 27

Power = energy transferred / time

Question 28

Kilowatt-hour

Answer 28

The energy transferred by a device with a power of 1W operating for a time of 1hour

Question 29

1kWh

Answer 29

3.6 MJ

Question 30

3.6 MJ

Answer 30

1kWh