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AS Physics Unit 1 > Chapter 4 - Electric Current > Flashcards

Chapter 4 - Electric Current Flashcards

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1
Q

How much charge flows through a bulb in 4 minutes if the current in the circuit is 0.25A.

A

Charge = current x time
0.25 x (4x60)
= 60C

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2
Q

How many electrons pass through a bulb in 4 minutes when the current flow is 0.25A. e = 1.6 x 10-19

A

Charge flowing = 60C
Number of electrons = charge /charge on one electron.
60/ 1.6 x 10-19 = 3.75 x 10 power 20

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3
Q

Define current.

A

The flow of charge or electrons.

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4
Q

Name the charge carriers in a metal.

A

The electron.

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5
Q

Name the charge carriers in a salt solution.

A

Ions.

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6
Q

What is the convention for the direction of current?

A

Positive to negative. Actual current flow is from negative to positive but electrons were not known when conventional current was agreed.

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7
Q

Define the coulomb.

A

The charge flow in one second when the current is 1 ampere.

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8
Q

Define potential difference.

A

Work done or energy transferred per unit charge.

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9
Q

What is the volt?

A

The unit for pd, equal to 1 joule per coulomb.

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10
Q

Define the emf of a source of electricity.

A

The electric energy produced per unit charge passing through the source.

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11
Q

What is the potential difference across a component if the work done is 50J when 5C passes through it.

A

Potential difference = W/Q = 50/5 = 10V.

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12
Q

Define power.

A

The rate of energy transfer. Unit Watt or Joule per second. Energy transferred per second.

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13
Q

Name the unit for charge.

A

Coulomb (C)

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14
Q

What is the unit for power?

A

The watt (W). The brightness of a bulb can be compared by calculating how much power each has. P = I x V.

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15
Q

What causes resistance?

A

Repeated collisions between the charge carriers and with each other as well as with the fixed ions in the material.

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16
Q

What is an ohm?

A

The unit for resistance, equal to one volt per ampere.

17
Q

Define Ohm’s law.

A

Potential difference across a conductor is proportional to the current through it, provided physical conditions e.g temperature do not change.

18
Q

What is the unit for resistivity?

A

Ohm metre.

19
Q

Define resistivity of a material.

A

Resistivity is the resistance multiplied by the cross sectional area of the material divided by its length. Quoting the equation and defining each term is enough.

20
Q

Describe the current - potential difference graph for a fixed resistor at constant temperature.

A

Straight line through the origin. The gradient corresponds to 1/R. Steeper gradient = smaller resistance.

21
Q

How is the resistivity of a material affected by its length?

A

Resistivity is a constant, specific to a material. It is not changed by length or cross sectional area. These factors affect the resistance of a wire, not its resistivity. Only the type of material affects resistivity values.

22
Q

How would you calculate the cross sectional area of a wire of diameter 0.5mm.

A

Either divide the diameter by 2 to get the radius.
Change the radius into metres (divide by 1000).
Then pi r2
Or divide d by 1000 then pi d2/4

23
Q

What is the unit for power?

A

The watt (W). The brightness of a bulb can be compared by calculating how much power each has. P = I x V.

24
Q

What causes resistance?

A

Repeated collisions between the charge carriers and with each other as well as with the fixed ions in the material.

25
Q

What is an ohm?

A

The unit for resistance, equal to one volt per ampere.

26
Q

Define Ohm’s law.

A

Potential difference across a conductor is proportional to the current through it, provided physical conditions e.g temperature do not change.

27
Q

What is the unit for resistivity?

A

Ohm metre.

28
Q

Define resistivity of a material.

A

Resistivity is the resistance multiplied by the cross sectional area of the material divided by its length. Quoting the equation and defining each term is enough.

29
Q

Describe the current - potential difference graph for a fixed resistor at constant temperature.

A

Straight line through the origin. The gradient corresponds to 1/R. Steeper gradient = smaller resistance.

30
Q

How is the resistivity of a material affected by its length?

A

Resistivity is a constant, specific to a material. It is not changed by length or cross sectional area. These factors affect the resistance of a wire, not its resistivity. Only the type of material affects resistivity values.

31
Q

How would you calculate the cross sectional area of a wire of diameter 0.5mm.

A

Either divide the diameter by 2 to get the radius.
Change the radius into metres (divide by 1000).
Then pi r2
Or divide d by 1000 then pi d2/4

32
Q

Describe how the resistance of a bulb changes with increasing potential difference.

A

The resistance increases as the wire in the bulb gets hot. This is due to greater collisions occurring between the flowing electrons and the fixed ions in the bulb wire.

33
Q

Describe the resistance of a diode when potential difference across it is varied .

A

In one direction, the resistance of the diode is very high and so no current flows through it. In the other direction, current flows after a certain potential difference is applied (known as the threshold potential difference, commonly 0.6V). After this the resistance is small and constant.

34
Q

What is a superconductor?

A

A material that has zero resistivity or resistance at or below a critical temperature.

35
Q

What is the critical temperature in superconductivity?

A

The exact temperature or below the temperature at which a material achieves superconductivity.

36
Q

Give a use for a superconducting material.

A

High power electromagnets generating strong magnetic fields for example transport.
Power cables transferring electrical energy without wasting energy.
LHC (particle accelerators)

37
Q

Why does the resistance of a bulb increase when the potential difference across it increases?

A

The bulb gets hotter as mobile electrons collide more with ions in the filament wire. Greater collisions = increased resistance.

38
Q

Calculate the charge flowing through a resistor during 5 minutes if the current is 0.2 A.

A

0.2 x (5x60) = 60C

AS Physics Unit 1 (6 decks)

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