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AQA A-Level Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

Current

A

The rate of flow of charge around a circuit

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2
Q

What is current caused by?

A

The movement of charged particles

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3
Q

An ideal ammeter has?

A

Zero resistance as it would change the current

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4
Q

Electrons flow from

A

The negative terminal to the positive terminal

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5
Q

Potential Difference

A

Work done per unit charge

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6
Q

An ideal voltmeter has ?

A

Infinite resistance

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7
Q

Resistance

A

A measure of opposition to the flow electrons through the component

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8
Q

Ohm’s Law

A

The pd across an ohmic conductor is directly proportional to the current flowing through it provided physical contact do not change

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9
Q

The gradient in an IV graph

A

Resistance = 1/gradient

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10
Q

IV characteristics of a resistor

A

Low resistance = Steep gradient
High resistance = Shallow gradient

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11
Q

Resistivity

A

Measure of how much opposition to the flow of electrons a conductor has

Constant value

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12
Q

Equation for resistivity

A

Resistivity = RA/L

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13
Q

The resistance of a wire is….

A

Inversely proportional to the area and inversely proportional to the length

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14
Q

Junction Rule

A

At any junction in the circuit, the total current entering the junction is equal to the total current leaving the junction

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15
Q

Loop rule

A

For any closed loop in a circuit, the sum of the emfs around the loop is equal to the sum of the potential drops

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16
Q

Power

A

The rate of energy transfer (Watts)

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17
Q

Power equation 1

A

Power = Current x Potential Difference

18
Q

Power equation used in series

A

P = I^2 x R

19
Q

Power Equation used in parallel

A

P = V^2/R

20
Q

Variable Resistor

A

Used to vary the current to a minimum when placed in series to a component

21
Q

Potential Divider

A

An arrangement of resistors

22
Q

Advantage and disadvantage of variable resistor

A

Adv - Easy to connect

Dis - Current through a component can never be = 0 - variable resistor is set to it’s max resistance

23
Q

Advantages and disadvantages of potential dividers

A

Adv - current through the component and Pd can be reduced to 0

Disadv - wastes power

24
Q

Charge is ?

A

The fundamental property of matter

25
Q

How to calculate the number of electrons in one Coulomb?

A

1/(charge of an electron)

Charge of an electron = 1.6 x 10^-19

26
Q

What can a variable potential divider be used for?

A

Change the output voltage with a fixed pd of supply

27
Q

Why does the resistance decrease with an increase in temperature in thermistors?

A

The number of charge carriers increases with an increase in temp as electrons break from from the atoms of the semiconductor

Therefore, there is a greater current and the resitance decrease

28
Q

Resistance- temp graph of thermistor

A

Decrease in resistance as temp increases is non linear

Almost like the letter L

29
Q

I/V characteristic of a thermistor

A

Thermistor with higher temp is steeper

Thermistor with lower temp is shallower

Constant temp = straight line

Higher temp (non constant) gradient increase

30
Q

Resistance of an LDR?

A

Decreases as light intensity increases

Same as thermistor but with light

31
Q

Superconductor

A

Material with 0 resistivity at and below the critical temperature

32
Q

Superconductivity

A

Property of superconductors

33
Q

Critical temperature

A

Temperature at and below which a superconductor has 0 resistivity

34
Q

Superconductors graph

Resistance-Temp graph

A

Straight line going along x axis

Shoots up at critical temperature

Then slow starts increasing gradient then quickly rises u

35
Q

When the temperature drops to the critical temperature?

A

The resistivity of the superconductor will suddenly drop to 0

36
Q

Superconductors can be used to make?

A

High power electromagnets and generate very strong magnetic fields

Used in particle accelerators and MRI scanners

Expel magnetic fields and repel magnets

37
Q

Electromotive force

A

Electrical energy per unit of charge produced by the source

EMF > Terminal PD

38
Q

Terminal pd

A

Electrical energy per unit charge that is delivered to external components

39
Q

Internal resistance

A

Resistance of materials within the battery

OR
The loss of potential difference per unit current in the source

40
Q

Equation for EMF

A

EMF = I(R + r)

EMF (V) - EMF Force
I (A) - Current
R (Ohms) - Resistance of components in the circuit
r (Ohms) - Internal resistance

41
Q

Other equation for EMF

A

EMF = V + Ir

Where V = terminal PD

AQA A-Level Physics (9 decks)

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