Flashcards in Unit 1: Electric Current and Direct Current Circuits Deck (81):

0

## What needs to happen in order to pass an electric current around a circuit?

### The circuit must be complete and there must be a source of potential difference.

1

## What is electric current?

### The rate of flow of charge.

2

## What is the current due to?

### The passage of charge carriers.

3

## What happens when a current passes through a metal?

### The charge carriers are electrons and they collide with each other and the fixed positive ions in the metal.

4

## What is conventional current?

### When the direction of current goes from the positive terminal to the negative terminal. It is opposite to the flow of electrons.

5

## What is the unit for current?

### Ampere

6

## What is the unit for charge?

### Coulomb

7

## What is one coulomb equal to?

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

8

## What is the symbol for charge?

### Q

9

## Why does an insulator not conduct electricity?

### Each electron is attached to an atom and cannot move away from it.

10

## What happens to the number of charge carriers in a semiconductor as temperature increases?

### The number of charge carriers also increases. The resistance therefore decreases.

11

## What happens in an intrinsic semiconductor?

### Electrons break free from the atoms of the semiconductor.

12

## What do electrons deliver from the battery to the components?

### Energy

13

## What does the battery supply each electron with?

### Electrical potential energy

14

## What is the work done by an electron equal to?

### The loss of potential energy.

15

## What is potential difference/voltage?

### The work done per unit charge.

16

## What is the emf of a source?

### The electrical energy produced per unit charge passing through the source.

17

## What is electrical energy produced equal to?

### Charge x emf

18

## What may happen due to a source's internal resistance?

### Some energy may be dissipated

19

## What effect does an electric current passing through a component have?

### A heating effect and a magnetic effect.

20

## What is power equal to?

### Energy/time

21

## How do you calculate power?

### IV

22

## What is the unit for power?

### Watt

23

## What is resistance?

### A measure of the difficulty of making current pass through the component.

24

## What is resistance caused by?

###
Repeated collisions between the charge carriers and the fixed positive ions in the metal.

25

## How can you calculate resistance?

### V/I

26

## What is the unit of resistance?

### Ohm

27

## How do you connect an ammeter?

### In series

28

## How do you connect a voltmeter?

### In parallel

29

## Why must no current pass through the voltmeter?

### So that the ammeter can accurately record the current passing through the component.

30

## What is the gradient of a pd/current graph?

### Resistance

31

## What is the gradient of a graph when current is plotted on the y axis and pd on the x axis?

### 1/R

32

## What is ohm's law?

### The pd across a metallic conductor is proportional to the current through it, provided the physical conditions do not change.

33

## What is resistance equal to in terms of resistivity?

### PL/A where p is resistivity (a constant)

34

## What is the unit of resistivity?

### Ohm metre

35

## What is a superconductor?

### A wire or device made of material that has zero resistivity at and below a critical temperature that depends on the material.

36

## Why does the current have no heating effect when it passes through a superconductor?

### There is no resistance therefore there is no potential difference.

37

## When does a superconductor lose its superconductivity?

### If it's temperature is raised above its critical temperature.

38

## What are superconductors used to make?

### High-power electromagnets that generate very strong magnetic fields and power cables that transfer electrical energy without wasting energy.

39

## What is a battery?

### A combination of cells.

40

## What is a cell?

### A source of electrical energy.

41

## What does a diode do?

### It allows current to flow in one direction only.

42

## What happens when a light-emitting diode conducts?

### It produces light.

43

## What is referred to as the forward direction?

### The direction in which the diode conducts.

44

## What is referred to as the reverse direction?

### The opposite direction to which the diode conducts.

45

## When is a diode used?

### To protect dc circuits.

46

## What happens to the resistance of a thermistor with increasing heat?

### It decreases.

47

## What happens to the resistance of a light dependent resistance with increasing light?

### It decreases.

48

## What can you use to measure the variation of current with pd?

### A potential divider to vary the pd from zero or a variable resistor to vary the current to a minimum.

49

## For a current and pd graph for a thermistor, which temperatures would provide a steeper gradient?

### High temperatures.

50

## Why does the graph for a filament bulb have a decreasing gradient?

### It's resistance increases as it becomes hotter.

51

## When does a silicon diode start to conduct?

### 0.6V

52

## Why does resistance increase when temperature does?

### The positive ions in the metal vibrate more when the temperature is increased. The charge carriers therefore cannot pass through as easily as before, it is said to have a positive temperature coefficient.

53

## What type of temperature coefficient does an intrinsic semiconductor have?

### Negative

54

## What is critical temperature also know as?

### Transition temperature.

55

## What is the case at any junction in a circuit?

### The total current leaving the junction is equal to the total current entering the junction.

56

## Do components use up current?

### No

57

## How is current distributed amongst more than two components in a series circuit?

### The current reaching each of the components is the same.

58

## What happens if he charge carriers lose energy?

### The potential difference is a potential drop

59

## What happens if the charge carriers gain energy?

### There is a potential rise

60

## What is the rule for pd in series circuits across the components?

### The total pd of the circuit is equal to the sum of the pd of each component.

61

## What is the sum of the emfs in a loop equal to?

### The sum of the pds.

62

## In a series circuit what is the total resistance equal to?

### The sum of the individual resistances.

63

## What is the total resistance in a parallel circuit given by?

### 1/R=1/R1+1/R2 ...

64

## What happens when a charge carrier loses energy due to a collision?

### The force of the pd causes it to accelerate until it collides with another positive ion.

65

## What are other ways of expressing power?

### I^2R or V^2/R

66

## Does power supplied depend on the direction of current?

### No

67

## How can you calculate energy transferred?

### I^2Rt

68

## Why is the terminal pd less than the emf?

### Internal resistance

69

## What is internal resistance?

### The loss of potential difference per unit current in the source when the current passes through the source.

70

## How can you calculate emf according to internal resistance?

### E=Ir+IR

71

## What is the power supplied by the cell equal to?

### IE=I^2R+I^2r

72

## When is maximum power delivered to a load?

### When load resistance is equal to the internal resistance.

73

## What is the gradient of a terminal pd/current graph equal to?

### Internal resistance

74

## What is the y intercept of a terminal pd/current graph equal to?

### The emf

75

## What happens to the terminal pd as the current increases.

### It decreases

76

## What is terminal pd?

### Emf at zero current

77

## How can you calculate terminal pd?

### E-Ir

78

## What does a potential divider consist of?

### Two resistors in series with a source of fixed potential difference.

79

## What is the ratio of pds across each resistor equal to?

### The resistance ratio of the two resistors.

80