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Alevel Physics AS/Alevel > Chapter 9 Energy Power and Resistance > Flashcards

Chapter 9 Energy Power and Resistance Flashcards

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1
Q

what is a battery?

A

two or more cells connected end to end

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2
Q

What is 1 volt?

A

1 joule of energy per unit charge

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3
Q

what is potential difference?

A

energy transferred from electrical energy to other forms per unit charge

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4
Q

what is the equation for potential difference?

A

P.d = work done / Charge

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5
Q

How do u measure potential difference?

A

Voltmeter

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6
Q

what is electromotive force (emf)?

A

energy transferred from chemical energy to electrical energy per unit charge

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7
Q

what is the equation for emf?

A

emf = work done / charge

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8
Q

how do u calculate energy transfer?

A

W=V x Q
W=emf x Q

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9
Q

what is the electron gun produce?

A

a narrow beam of electrons

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10
Q

what is thermonic emmision?

A

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

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11
Q

how does an electron gun source electrons?

A

by using electric current to heat a small metal filament

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12
Q

what is kinetic energy equation?

A

KE = 1/2 mv^2

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13
Q

word done on electrons is equal to?

A

eV

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14
Q

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

A

eV = 1/2 m v^2

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15
Q

what is the law of conservation of energy?

A

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

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16
Q

what is the unit for resistance?

A

Ohm

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17
Q

what is Ohms law?

A

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

18
Q

what is the equation for ohms law?

A

R = Voltage / Current
R = V / I

19
Q

What are IV charcteristics used for?

A

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

20
Q

what are the IV characteristics of a filament lamp?

A

the Potential difference is not directly proportional to current

It does not obey ohms law

the resistance is not constant

21
Q

what is a unique property of diodes?

A

it only allows current in one direction

22
Q

what are LEDs used for in a circuit?

A

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

23
Q

what are the IV characteristics of a Diode ?

A

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

it does not obey ohms law

the resistance is not constant

24
Q

What is the term resistivity used to describe?

A

The electrical property of a material

25
Q

What makes different components of copper have different resistances?

A

their lengths and cross sectional areas

26
Q

Why is Resistance directly proportional to Length of a wire?

A

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

27
Q

Why is resistance inversely proportional to Area?

A

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

28
Q

if Resistance is equal to Resistivity what is the equation?

A

R = pL/A

29
Q

What is the unit for Resistivity

A

Ohm Meter

30
Q

How can you determine Resistivity?

A

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

31
Q

what is the gradient of resistance over length graph

A

Resistivity / Area

32
Q

What are thermistors used for?

A

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

33
Q

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

A

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

34
Q

What is electrical power?

A

the rate of energy transferred by electrical components

35
Q

what is the equation for electrical power?

A

Electrical power = p.d. x current

36
Q

what are the additional equation for power?

A

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

37
Q

What is unit for Power

A

Watt (W)

38
Q

what is a KiloWatt-hour

A

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

39
Q

what is 1KW h equivalent to

A

3.6Mjoules

40
Q

Define resistance

A

P.d /voltage per unit current

Alevel Physics AS/Alevel (11 decks)

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