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ALevel Physics NEW > Section 6 - Electricity > Flashcards

Section 6 - Electricity Flashcards

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1
Q

Define current

A

Rate of flow of charge

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2
Q

What is the unit of current?

A

A - Ampere

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3
Q

What is the unit of charge?

A

C - Coulomb

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4
Q

Define coulomb

A

The amount of charge that passes in 1 second of the current is 1 ampere

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5
Q

How do you measure current, and how do you connect the component?

A

With an ammeter in series

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6
Q

Define potential difference

A

Work done per unit charge moved

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7
Q

How do you measure voltage, and how do you connect the component?

A

With a voltmeter in parallel

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8
Q

Define a volt

A

When one joule of energy is moving 1 coulomb of charge through a component

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9
Q

Define resistance

A

A potential difference of 1 volt making a current of 1 amp generates 1 Ohm, R = V / I

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10
Q

State Ohm’s law

A

Provided the physical conditions are kept constant, the current through an ohmic conductor is directly proportional to the p.d across it

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11
Q

What do I/V graphs show in terms of resistance?

A

How it varies

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12
Q

On an I/V graph for a resistor, what does a steep and shallow gradient represent?

A

Steep means low resistance

Shallow means steep resistance

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13
Q

On an V/I graph for a resistor, what does a steep and shallow gradient represent?

A

Steep means high resistance

Shallow means low resistance

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14
Q

Describe the curve for a filament lamp on an I/V and V/I graph

A

I/V - Starts shallow but gets steeper curve. Only touches the origin type cubic
V/I - Starts steep and gets shallower. Point of inflexion type cubic as stays at origin for a bit

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15
Q

What is a filament?

A

A coiled up length of wire

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16
Q

State an application for semi conductors

A

Sensors, diodes and thermistors

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17
Q

Why are semiconductors good sensors?

A

When energy is supplied, more charge carriers are released

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18
Q

What does the resistance of a thermistor depend on?

A

Temperature

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19
Q

What happens as the temperature of a thermistor increases?

A

Resistance decreases

20
Q

Describe the resistance-temperature graph for a thermistor

A

Top left to bottom right inward curve

21
Q

Describe the I/V and V/I graph for a thermistor

A

I/V - Starts steep and gets shallower
V/I - Starts shallow and gets steeper
OPPOSITE TO FILAMENT LAMP

22
Q

What are diodes designed to do?

A

Let current flow in 1 direction

23
Q

Describe the I/V and V/I graph for a diode

A

I/V - At 0 until about 0.6V then sharp spike

V/I - Sharp increase and then steady upward sloping line

24
Q

What 3 things determine resistance?

A

Length - Longer the wire, the lower the current
Area - The wider the wire, the larger the current
Resistivity - Depends on material

25
Q

Define resistivity

A

The resistance of a 1m wire with a 1m^2 of cross sectional area

26
Q

What is the unit of resistivity?

A

Ohm meters

27
Q

Describe the process to find the resistivity of a wire

A
  • Use micrometer to measure diameter in multiple places
  • Take an average and find area of wire
  • Test wire should be clamped where the ruler reads 0
  • Attach the flying lead to the clamped wire and record the length of the wire
  • Record the voltmeter and ammeter reading and calculate resistance
  • Repeat and draw a graph. Multiply the area by the gradient = resistivity
28
Q

State uses of superconductors

A
  • Power cables transmit electricity with no loss of power
  • Strong electromagnets don’t need a constant power source
  • Electronic circuits work really fast
29
Q

Define power

A

The rate of transfer of energy

30
Q

State the extra power equations you need to know

A 
P = I^2R
P = V^2 / R
31
Q

State the energy equation you need to know

A

E = IVt

32
Q

Where does resistance come from?

A

Electrons colliding with atoms and losing energy to other forms

33
Q

What makes electrons move in a battery?

A

Chemical energy

34
Q

What is emf?

A

The amount of electrical energy the battery produces for each coulomb of charge

35
Q

What is the terminal p.d?

A

The energy transferred when 1 coulomb of charge flows through the load resistance

36
Q

What are lost volts?

A

Energy wasted per coulomb overcoming the internal resistance

37
Q

What is the terminal p.d if there is no internal resistance?

A

The same as the emf

38
Q

How can you calculate the total emf in a series circuit?

A

By adding the their individual emfs

39
Q

How can you calculate the total emf in a parallel circuit?

A

The total emf of the cells is the same size as the emf of each of the individual cells

40
Q

Does charge get used up in a circuit?

A

No

41
Q

State Kirchhoff’s first law

A

Total current entering a junction = total current leaving it

42
Q

State Kirchhoff’s second law

A

Total emf around a series circuit = sum of pds across each component

43
Q

What does a potential divider do?

A

It splits the pd across the voltage source into a ratio of resistances

44
Q

What is the use for a potential divider?

A

Supply a pd between 0 and the pd across the voltage source

45
Q

What is a use for a variable resistor?

A

To vary voltage

46
Q

What is the use of a potentiometer?

A

Using a variable resistor to give a variable voltage

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