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Physics - Unit Two > Currents in Electrical Circuits > Flashcards

Currents in Electrical Circuits Flashcards

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1
Q

What is a conductor?

A

A material that an electrical charge can easily pass through. Metals are good conductors thanks to their delocalised electron.

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2
Q

What is an insulator?

A

A material that electrical charges cannot easily move through. Plastics and rubber are good insulators.

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3
Q

What is a static charge?

A

An electric charge that cannot move.

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4
Q

Where are static charges usually found?

A

In insulators

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5
Q

How do insulators gain a static charge?

A

When some insulating materials are rubbed together, electrons are scraped off one onto the other. The one that loses the electrons gains a positive static charge and the one that gains electrons gains a negative static charge.

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6
Q

What does it mean if a circuit is complete?

A

The wire gird from one end of the cell/battery to the other.

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7
Q

How must voltmeters be connected to a circuit?

A

In parallel across the component you are measuring.

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8
Q

How must an ammeter be connected to a circuit?

A

In series

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9
Q

What is an electric current?

A

A flow of electric charge.

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10
Q

What side of a cell/battery is positive and which is negative?

A

The big end is positive and the small end is negative.

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11
Q

What way does a charge travel through a circuit?

A

From positive to negative

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12
Q

What is the size of a current? What is it measured in?

A

The rate of flow of charge. It’s measured in amperes, A.

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13
Q

What is the formula for current?

A

Q
I = —-
t

I = Current (A)

Q = Charge (C - coulombs)

t = Time (secs)

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14
Q

What is potential difference?

A

The driving force that pushes the current round the circuit. It’s the work done per coulomb of charge.

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15
Q

What is the formula for potential difference?

A

W
V = ——
Q

V = Potential difference (V)

W = Work done (J)

Q = Charge (C)

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16
Q

What is resistance?

A

Anything in a circuit that reduces the flow of current.

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17
Q

What is resistance measured in?

A

Ohms, Ω.

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18
Q

What is Ohm’s law?

A

V = I x R

V = Potential difference (V)

I = Current (A)

R = Resistance (Ω)

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19
Q

What does a variable resistor do?

A

You can change its resistance.

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20
Q

How would one get negative readings for potential difference?

A

Switch the way round the wires are connected to the power source. This means that the current will flow in the opposite direction.

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21
Q

What does a current-potential difference graph show?

A

How current varies with potential difference.

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22
Q

What do current-potential difference graphs look like for resistors?

A

Straight line graphs - the current through a resistor is directly proportional to potential difference.

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23
Q

What does the current-potential difference graph look like for a filament lamp?

A

S- shaped. This is because as more current flows through the filament it heats up which makes it more difficult for the current to get through.

24
Q

How does temperature affect resistance?

A

When a component gets hotter, its ions begin to move which makes it harder for the charge to make it through as resistance increases.

25
Q

Why do most components have a limit to the amount of current they can carry?

A

Because current increases the temperature of the component meaning eventually its resistance will increase to the point where the current can no longer fit any more charge through.

26
Q

What is the difference between a cell and a battery?

A

A battery contains multiple cells.

27
Q

What does the symbol for an ammeter look like?

A

A circle within A in it.

28
Q

What does the symbol for a voltmeter look like?

A

A circle with a V in it.

29
Q

What does the symbol for a resistor look like?

A

A hollow rectangle.

30
Q

What does the symbol for a variable resistor look like?

A

A rectangle with an arrow going through it.

31
Q

What is a diode?

A

A component that only lets current move freely in one direction through it. This because there’s a very high resistance in the other direction.

32
Q

What does the symbol for a diode look like?

A

A circle with an arrow in it indicating the direction of current flow through it.

33
Q

What does the I-V graph for a diode look like?

A

It is at 0 for negative values and then goes up very steeply on the positive side.

34
Q

What do LEDs do?

A

Light Emitting Diodes emit light when a current flows through it in the forward direction. They can be used to indicate the presence of a current in a circuit.

35
Q

What does the symbol for an LED look like?

A

A circle with an arrow in it indicating the flow of current through it. There are two arrows pointing away from it indicating that it emits light.

36
Q

What three advantages do LEDs have over filament bulbs?

A
  • LEDs have a much longer lifetime
  • LEDs are much more energy efficient as they don’t produce as much waste heat energy
  • LEDs require a much smaller current so they are cheaper to run
37
Q

What are two disadvantages of LEDs?

A
  • They are much more expensive than filament bulbs

* You often need multiple LEDs to produce the same amount of light as a filament bulb

38
Q

What is the symbol for a filament bulb?

A

A circle with a cross through it

39
Q

What is an LDR?

A

A light dependent resistor is a resistor that varies its resistance with light intensity:

  • In bright light, resistance falls
  • In darkness, resistance is very high
40
Q

What I the symbol for an LDR?

A

A circle with a hollow rectangle inside it to represent the resistor. There are two arrows pointing toward the circle to represent the light going in.

41
Q

What are two used of LDRs?

A
  • Streetlights

* Burglar alarms

42
Q

What is an NTC Thermistor?

A

A resistor whose resistance decreases as temperature increases.

43
Q

What is the symbol for a thermistor?

A

A resistor with a line going through it. The line is flat on one end.

44
Q

What is a use of thermistors?

A

Thermostats

45
Q

What is a series circuit?

A

A circuit in which all the components are connected in line. If one were to be removed the circuit would be broken and it would stop working.

46
Q

How does one work out the potential difference in a series circuit?

A

Add up the potential differences of all the cells OR add up the potential difference across each component.

47
Q

What is current like in a series circuit?

A

The same in all parts of the circuit.

48
Q

How does one work out the total resistance of a series circuit?

A

Add up the individual resistances of each component.

49
Q

What is a parallel circuit?

A

A circuit in which components have their own branch meaning that if you were to disconnect one of the components it would have no effect on the others.

50
Q

What is potential difference like in parallel circuits?

A

The same across every branch as each branches potential difference is the same as that of the source.

51
Q

What is the symbol for an open switch?

A

Two dots with a diagonal line not quite connecting them.

52
Q

What is the symbol for a closed switch?

A

Two dots connected by a straight line.

53
Q

What is current like in a parallel circuit?

A

It is split across the branches. To understand the total current you have to add together the current on each branch.

54
Q

What is the symbol for a fuse?

A

A straight line going through a rectangle.

55
Q

What is the symbol for a motor?

A

A circle with an M in it.

Physics - Unit Two (6 decks)

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