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Physics A Level > 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

It is a group of cells in series or parrallel

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2
Q

LEARN THE SYMBOLS FOR ELECTRIC CIRCUITES

A

DO IT

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3
Q

What is a volt?

A

It is the potential difference between two points on a circuit

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4
Q

What is the unit and SI derivation of a volt?

A

The unit is Volts (V) and si units JC^-1

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5
Q

What is the equation for a volt?

A

Volt = Work / Coulombs

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6
Q

How is a volt meter used?

A

It is used in parallel with the circuit

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7
Q

What is electromotive force? What is the symbol?

A

This is used to describe when work is being done on the charge carriers as they pass through a battery. It is the energy gained per coulomb passing through a battery so has the units Volts.
The symbol is ε

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8
Q

What is the equation for electromotive force?

A

ε = W / Q

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9
Q

How is energy transfer calculated from voltage?

A

Work = Voltage x coulombs
or
Work = Electromotive force x coulombs

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10
Q

How does an electron gun work?

A

A hot filament in a vacuum is heated and given a negative charge (cathode) then an anode is put at the other end of the vacuum and the electrons released from the cathode are attracted to the anode and accelerate

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11
Q

What is the equation for an electron gun?

A 
eV = 1/2mv^2
e = elementary charge
V = potential difference of the cathode and anode
m = mass
v = velocity
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12
Q

How can the acceleration of electrons be changed?

A

By changing the potential difference of the cathode and anode

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13
Q

What is the most important equation for electricity?

A

V = IR

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14
Q

What is resistance?

A

It is a measure of how hard it is for current to flow through a material

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15
Q

What is the equation for resistance?

A

R = V / I

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16
Q

What is the unit for resistance? and SI derivative and symbol?

A

The ohm
V A^-1
Ω

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17
Q

What is ohms law?

A

As long as temperature remains constant, the current through a material is directly proportional to the voltage across it.

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18
Q

How does temperature affect resistance?

A

The wire gets hot because of collisions between electrons and the positive ions in the wire. This heat causes to positive ions to vibrate more and this causes the frequency of collisions to increase causing more collisions. So as temperature increases so does the reisistance

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19
Q

What material is used for fillaments?

A

Tungsten

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20
Q

What does the IV graph for a resistor look like?

A

It is a straight line through the origin where the gradient is 1/resistance
It is ohmic because it obeys ohms law

21
Q

Filament lamps

A

The gradient starts even (middle e.g. 1 ) and then flattens out as the voltage increases. As the voltage increases the resistance increases
It is non ohmic because the gradient is not constant

22
Q

What is a diode?

A

It is a component that only allows current to flow in one direction. The resistance to current in the reverse direction is very high

23
Q

What is an LED?

A

It is light emitting diode that is made from a material the releases light when electricity passes through it.

24
Q

What is special about the light from an LED?

A

It is of a specific single wavelength

25
Q

What does the IV curve for a diode look like?

A

It starts flat (high resistance) and then past the threshold voltage the gradient increases and becomes much steeper (lower resistance)
Then when the current is in the reverse direction the resistance is almost infinate.

26
Q

What are factors that affect the resistance of a wire?

A

Material
Length of wire
Cross-sectional area
Temperature

27
Q

What are praportionalities that can be drawn from the resistance of a wire?

A

R ∝ L

R ∝ 1/A

28
Q

What is resistivity?

A

resistance refers to a specific component and resistivity is used to describe the electrical properties of a material
It is the resistance of a component multiplied by its cross sectional area per unit length

29
Q

What is the symbol of resistivity? and what is its unit?

A

ρ and units Ωm

30
Q

What is the equation for resistivity?

A

R = ρL / A

31
Q

What affects resistivity?

A

The temperature

32
Q

What is the order of resistivity for conductors?

A

10^-8 Ω

33
Q

What is the order of resistivity for insulators?

A

10^16 Ω

34
Q

What is a negative temperature coefficient?

A

It means that as the temperature increases, the resistance drops

35
Q

What is a thermistor?

A

It is a component thats resistance changes with temperature

36
Q

What are thermistors made from?

A

They are made from semiconductors with a negative temperature coefficient

37
Q

What are uses for thermistors?

A

Thermometers
Thermostats and air conditioning
Inside computers
Car engines

38
Q

What graph can be made from placing a resistor in hot water with a thermometer?

A

The Resistance of the thermistor can be calculated with a ammeter and a voltmeter and then plotted against temperature as the water cools

39
Q

What are the IV characteristics of a thermistor?

A

They are non ohmic and produce a graph oposite to a filament lamp. The gradient increases (so resistance decreases) as the voltage increases.

40
Q

What is an LDR and what does it do?

A

Light dependent resistor

A component thats resistance changes as light is shone on it

41
Q

What are the properties of an LDR?

A

In the dark they have a high resistance

In the light they have a low resistance

42
Q

How does distance from a light source affect an LDR?

A

The further the distance the lower the light intensity so the further the distance the higher the resistance

43
Q

What is the equation to work out electrical power?

A

P = VI

44
Q

What is the unit for power?

A

Watts (W)

45
Q

What are alternative equations for electrical power?

A 
P = I^2R
P = V^2 / R
46
Q

How is the P = IV derrived?

A 
P = Work / Time
P = Voltage x Coulombs / Time
P = Voltage x Current
47
Q

How is energy transferred calculated?

A

Watts x time = Joules transferred (Work)

Work = VIt

48
Q

What is the definition of a kilowatt hour?

A

It is the energy transferred by a 1 kilowatt device operating for 1 hour

49
Q

What is the symbol for kilowatt hour?

A

kWh

Physics A Level (27 decks)

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