Chapter 9 Energy Power and Resistance

Question 1

what is a battery?

Answer 1

two or more cells connected end to end

Question 2

What is 1 volt?

Answer 2

1 joule of energy per unit charge

Question 3

what is potential difference?

Answer 3

energy transferred from electrical energy to other forms per unit charge

Question 4

what is the equation for potential difference?

Answer 4

P.d = work done / Charge

Question 5

How do u measure potential difference?

Answer 5

Voltmeter

Question 6

what is electromotive force (emf)?

Answer 6

energy transferred from chemical energy to electrical energy per unit charge

Question 7

what is the equation for emf?

Answer 7

emf = work done / charge

Question 8

how do u calculate energy transfer?

Answer 8

W=V x Q
W=emf x Q

Question 9

what is the electron gun produce?

Answer 9

a narrow beam of electrons

Question 10

what is thermonic emmision?

Answer 10

when electrons gain kinetic energy to escape from the surface of the metal

Question 11

how does an electron gun source electrons?

Answer 11

by using electric current to heat a small metal filament

Question 12

what is kinetic energy equation?

Answer 12

KE = 1/2 mv^2

Question 13

word done on electrons is equal to?

Answer 13

eV

Question 14

what is the expression relating work done on electrons to KE?

Answer 14

eV = 1/2 m v^2

Question 15

what is the law of conservation of energy?

Answer 15

the total energy of the system is constant, even if energy has been converted from one form to another

Question 16

what is the unit for resistance?

Answer 16

Ohm

Question 17

what is Ohms law?

Answer 17

the resistance of a component when a p.d of 1 V is produced per ampere of current

Question 18

what is the equation for ohms law?

Answer 18

R = Voltage / Current
R = V / I

Question 19

What are IV charcteristics used for?

Answer 19

to show the relationship between current in a component and potential difference across it?

Question 20

what are the IV characteristics of a filament lamp?

Answer 20

the Potential difference is not directly proportional to current

It does not obey ohms law

the resistance is not constant

Question 21

what is a unique property of diodes?

Answer 21

it only allows current in one direction

Question 22

what are LEDs used for in a circuit?

Answer 22

they light up when there is current in them showing that part of the circuit is live

Question 23

what are the IV characteristics of a Diode ?

Answer 23

p.d of a diode in not directly proportional to current

it does not obey ohms law

the resistance is not constant

Question 24

What is the term resistivity used to describe?

Answer 24

The electrical property of a material

Question 25

What makes different components of copper have different resistances?

Answer 25

their lengths and cross sectional areas

Question 26

Why is Resistance directly proportional to Length of a wire?

Answer 26

for given current V is directly proportional L of wire V is directly proportional to R Therefore R directly proportional to L

Question 27

Why is resistance inversely proportional to Area?

Answer 27

for a given voltage I is directly proportional to A I is inversely proportional to R Therefore R is inversely proportional to A

Question 28

if Resistance is equal to Resistivity what is the equation?

Answer 28

R = pL/A

Question 29

What is the unit for Resistivity

Answer 29

Ohm Meter

Question 30

How can you determine Resistivity?

Answer 30

by investigating how resistance of a wire varies with it's length

Question 31

what is the gradient of resistance over length graph

Answer 31

Resistivity / Area

Question 32

What are thermistors used for?

Answer 32

-to control heating / air conditioning -to monitor engine tempertures -to measure tempertures in wide variety of electrical devices like toasters and kettles

Question 33

What is a key difference in IV characteristics in a thermistor compared to a filament lamp?

Answer 33

Similar to a filament lamp as current increases temperture increases but in a thermistor this leads to a drop in resistance due to number density in charge carriers increasing whereas in a filament lamp resistance would increase

Question 34

What is electrical power?

Answer 34

the rate of energy transferred by electrical components

Question 35

what is the equation for electrical power?

Answer 35

Electrical power = p.d. x current

Question 36

what are the additional equation for power?

Answer 36

P = I^2 R P = V^2 / R P - W / T P - V I t

Question 37

What is unit for Power

Answer 37

Watt (W)

Question 38

what is a KiloWatt-hour

Answer 38

energy transferred by a device with power 1KW for a time of 1hr

Question 39

what is 1KW h equivalent to

Answer 39

3.6Mjoules

Question 40

Define resistance

Answer 40

P.d /voltage per unit current