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ALevel Physics > Chapters 8, 9, and 10 - Electricity > Flashcards

Chapters 8, 9, and 10 - Electricity Flashcards

They are all about electricity so it makes it easier for me to put them into one deck

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1
Q

What is Current?

A

The rate of flow of charge

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2
Q

What is Charge?

A

A property of matter which causes it to feel a force when near electrically charged matter

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3
Q

What is Potential Difference?

A

The energy transferred from electrical energy to other forms per unit charge

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4
Q

What is Kirchoff’s First Law?

A

The sum of the current entering a junction is equal to the sum of the sum leaving the current

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5
Q

What is mean drift velocity?

A

The average velocity of charge carriers moving.

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6
Q

What are the three factors that affect mean drift velocity?

A

Current
Number Density
Cross sectional area of the wire

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7
Q

Why do electrons move slowly?

A

Due to the large number of random collisions with the fixed positive ions.

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8
Q

What is the number density of a material?

A

The number of charge carriers that are free to move in a material per unit volume.

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9
Q

How does decreasing cross-sectional area affect mean drift velocity?

A

The current must stay the same, so the drift velocity must increase in order for that to happen.

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10
Q

What is the circuit symbol for a variable resistor?

A

rectangle with a diagonal arrow going through it

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11
Q

What is the circuit symbol for a fuse?

A

rectangle with the wire going through it

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12
Q

What is the circuit symbol for a thermistor?

A

rectangle with a line that starts straight and then goes diagonal through it.

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13
Q

What is the circuit symbol for a LDR?

A

rectangle with two arrows pointing at it.

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14
Q

What is the circuit symbol for a LED?

A

Diode symbol with two arrows pointing away from it

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15
Q

What is the circuit symbol for a capacitor?

A

Two vertical lines with a gap between them

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16
Q

What is one volt?

A

1J of energy is transferred per unit of charge

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17
Q

What is e.m.f?

A

Electromotive force, when work is done on the charge carriers. The energy converted from another form into electric energy.

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18
Q

What is thermionic emission and what is it used by?

A

Use by electron guns. When electrons are emitted through the action of heat.

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19
Q

How does an electron gun work?

A

A metal filament is heated by an electric current. Some of the electrons gain enough kinetic energy to escape from the surface of the metal.

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20
Q

What is Ohm’s law?

A

V = IR

For a component at a constant temperature, the current in the wire is directly proportional to the p.d across its ends.

21
Q

What happens when the temperature of a wire increases and why?

A

The resistance increases. This is because the positive ions in the wire have more energy and so vibrate with greater amplitude. Therefore the frequency of collisions between the ions and the charge carriers also increases.

22
Q

What is the I - V characteristic for a fixed resistor?

A

A straight line through the origin

23
Q

A resistor can be described as an ohmic what?

A

conductor

24
Q

The potential difference across a fixed resistor is directly proportional to what?

A

The current in the resistor

25
Q

What is the I -V characteristic of a filament lamp?

A

A line that starts straight but then curves towards the x axis

26
Q

What is the I - V characteristic of a diode?

A

On one side the line is flat, on the other it curves upwards

27
Q

What are the four factors that affect resistance of a wire?

A

Temperature
Material
Length
Cross-sectional area

28
Q

The resistance of a wire is directly proportional to what?

A

Length

29
Q

The resistance of a wire is inversely proportional to what?

A

cross-sectional area

30
Q

What is the difference between resistance and resistivity?

A

Resistance refers to a specific component, while resistivity is used to refer to the electrical property of a material.

31
Q

As the temperature of a thermistor increases the resistance…

A

decreases

32
Q

How does an LDR work?

A

The LDR is made of a semiconductor in which the number density of charge carriers is based on the intensity of light. The higher the intensity, the lower the resistance of the LDR.

33
Q

What is Kirchoff’s second law?

A

The sum of the electromotive forces is equal to the sum of the potential differences around a closed loop.

34
Q

What Law is related to Kirchoff’s second law?

A

Conservation of energy

35
Q

How does Kirchoff’s second law apply to a series circuit?

A

The p.d is spread between components so that the components with greater resistance have get a greater proportion of the p.d

36
Q

How does Kirchoff’s second law apply to a parallel circuit?

A

The total p.d across each path must be equal to the total e.m.f. In each path the e.m.f is spread across each component so that those with the highest resistance get a greater proportion of the total e.m.f.

37
Q

What is the terminal p.d?

A

The p.d measured at the terminals of the power source

38
Q

How do you find the lost volts in a circuit?

A

e.m.f - terminal p.d

39
Q

What causes lost volts?

A

Work has to be done on the charge carriers as they move through the power source. Not all of the energy is transferred to the charge carriers, and is instead lost to heat.

40
Q

How do sensing circuits work?

A

A fixed resistor and a variable resistor are connect in series. An output component is then connect in parallel across one of the resistors. The voltage across each resistor will change based on resistance of the resistors, as the resistor with the highest resistance will have a greater proportion of the total p.d.

41
Q

What is a thermistor made from?

A

A semiconductor with a negative temperature coefficient. As the temperature increases, more charge carriers are released, lowering the resistance.

42
Q

What direction is conventional current?

A

From positive to negative

43
Q

What direction do electrons travel in?

A

From negative to positive

44
Q

What is number density?

A

The number of free charge carriers per unit volume

45
Q

Why do electrons move faster in narrower wires?

A

The current, elemental charge and number density remains constant, but the cross sectional area in the wires is smaller. Therefore the mean drift velocity of the must increase to keep the current the same.

46
Q

The length of a wire is directly proportional to its…

A

Resistance

47
Q

The cross sectional area of a wire is inversely proportional to its…

A

Resistance

48
Q

What is resistivity?

A

A property of a material that describes how much resistance a component made from that material would have.

ALevel Physics (18 decks)

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