4.2 - Energy, Power and Resistance

Question 1

What is potential difference?

Answer 1

The work done per unit charge between two points

Question 2

What is the SI unit for potential difference?

Answer 2

Volt (V)

Question 3

What units are equivalent to the volt?

Answer 3

Joules per Coulomb (JC^-1)

Question 4

What is EMF?

Answer 4

Electromotive force, the work done per unit of charge supplied to the charge carriers

Question 5

How is a voltmeter connected?

Answer 5

In parallel

Question 6

What is the resistance of an ideal voltmeter?

Answer 6

Infinite

Question 7

What is thermionic emission?

Answer 7

The emission of electrons from the surface of a heated metal

Question 8

What is the work done on an electron when it passes through a p.d of V volts?

Answer 8

eV where e is the charge on the electron

Question 9

What is Ohm’s law?

Answer 9

For a metallic conductor at a constant temperature the p.d. is proportional to current

Question 10

What is electrical resistance?

Answer 10

The opposition of an object to the flow of current through it

Question 11

How id resistance calculated?

Answer 11

V/I

Question 12

What units are equivalent to an Ohm?

Answer 12

VA^-1

Question 13

Why does resistance increase with temperature?

Answer 13

The amplitude of lattice ion vibrations increases causing more frequent collisions between electrons and lattice ions, leading to the electrons doing more work as they move through the wire

Question 14

Why does current flow lead to heating in components?

Answer 14

Electrons collide with the lattice ions and transfer some of their kinetic energy to the lattice ions vibrations

Question 15

What is an ohmic conductor?

Answer 15

An object for which p.d is proportional to current

Question 16

What is meant by the threshold pd of a diode?

Answer 16

The pd at which resistance starts to fall rapidly as pd increases

Question 17

What are the units of resistivity?

Answer 17

Ωm

Question 18

What is ρ in R=ρL/A?

Answer 18

the resistivity of the metal

Question 19

What is L in R=ρL/A

Answer 19

The length of the wire

Question 20

What is A in R=ρL/A

Answer 20

the cross sectional area of the wire

Question 21

As a metal gets hotter what happens to its resistivity?

Answer 21

It increases

Question 22

What is meant by a negative temperature coefficient component?

Answer 22

One in which the resistance drops as temperature increases

Question 23

Why does the resistance of a thermistor fall as temperature increases?

Answer 23

The number density of charge carriers increases

Question 24

What are thermistors commonly used in?

Answer 24

Temperature sensors

Question 25

Why does the resistance of an LDR change as light intensity changes?

Answer 25

Light intensity increases the number density of charge carriers in the LDR

Question 26

What are LDRs commonly used in?

Answer 26

Light intensity sensors

Question 27

What happens to the resistance of an LDR as light intensity increases?

Answer 27

It decreases

Question 28

What is a kilowatt-hour (kWh)?

Answer 28

The energy supplied when 1kW of power is supplied for 1 hour

Question 29

How many joules are equivalent to a kWh

Answer 29

3.6MJ