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LGS GCSE OCR Physics > P3.2 - Simple Circuits > Flashcards

P3.2 - Simple Circuits Flashcards

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1
Q

How can objects become charged?

A

Objects can be charged by transferring electrons to/from them, by the force of friction…simply by rubbing.

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2
Q

What do you need to make current flow in a circuit?

A

Current can only flow if there exists a difference in voltage between two points; if there exists a potential difference.

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3
Q

What is the result of charges being easier to detect?

A
  • Electrons are incredibly difficult to count.
  • Charge is easier to detect.
  • Therefore, current and potential difference are
    always defined in terms of charge flow (not
    electron flow).
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4
Q

What is voltage?

A

Voltage is a measure of the energy carried by the current per coulomb of charge.

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5
Q

What is potential difference?

A
  • Potential difference is the difference in voltage
    between two points.
  • Potential difference is a measure of work done per
    coulomb of charge
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6
Q

What is the formula for potential difference?

A
  • V = W/Q
  • V = Potential difference - V
  • W = Work done - J
  • Q = Charge - C
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7
Q

How is potential difference measured across components?

A

Potential difference are measured across components in a circuit using a voltmeter.

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8
Q

What does the p.d. across a component indicate?

A

The p.d. across a component indicates how much energy (per coulomb of charge) was transferred by the current as it passed through the component.

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9
Q

What is resistance?

A

Resistance is the opposition to the passage of charge.

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10
Q

What is the idea of resistance?

A
  • In a wire component, ions vibrate up and down.
    -These vibrating ions will get in the way of the
    passing electrons, stopping them from flowing,
    reducing the current.
  • The faster the ions vibrate (the hotter the wire) or
    the bigger the ions, the greater the resistance
    encountered, and the smaller the current flowing
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11
Q

What does a higher resistance mean?

A

The higher the resistance, the more energy transferred by the current as it passes through the resistance.

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12
Q

What is the fundamental equation of electricity?

A
  • V=IR
  • V = Potential difference - Volts - V
  • I = Current - A
  • R = Resistance - ohms
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13
Q

What is a series circuit?

A
  • A series circuit is one in which the electrons must
    travel through every component.
  • The electrons get ““no choice”” - Must transfer
    energy to the same components
  • The circuit has no branches, but is just one loop.
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14
Q

How is the current in a series circuit?

A

The current through every component in a series circuit is the same.

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15
Q

How is the resistance in a series circuit?

A

The total resistance in a series circuit is the sum of all the component resistances.

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16
Q

How is the potential difference of a series circuit?

A
  • The p.d. across components in a series circuit is
    shared out.
  • The greater the resistance, the greater the share
    of the total p.d. it has across it.
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17
Q

What is a parallel circuit?

A
  • A parallel circuit is one in which the electrons don’t
    travel through the same components.
  • The electrons get ““a choice”” - transfer energy to
    different components.
  • A parallel circuit has branches.
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18
Q

How is the potential difference in a parallel circuit?

A

The p.d. across components in a parallel circuit is the same.

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19
Q

How is resistance in a parallel circuit and why?

A
  • The total resistance in a parallel circuit is less than
    the component with the smallest resistance in the
    circuit.
  • The are more paths for the current to flow through.
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20
Q

How is current in a parallel circuit?

A
  • The current in a parallel circuit is split between
    components/branches.
  • The greater the resistance of the component, the
    less current through it.
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21
Q

What do variable resistors do?

A

Variable resistors change the current in a circuit by varying its resistance.

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22
Q

Why is potential difference not a dependant variable?

A

The potential difference for a circuit is a constant set by the battery/cell of a circuit.

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23
Q

Why are you unlikely to be injured by an electric current in your house?

A

The p.d. of main circuits are 230V which is much lower than required to give rise to a current of 1A.

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24
Q

What is an I-V graph?

A

An I-V graph is a plot of current, I (y-axis) against p.d., V (x-axis).

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25
Q

What does the gradient of an I-V graph give?

A
  • The gradient of an I-V graph gives the opposite of
    resistance.
  • A diagonal straight line = Constant resistance.
  • A steep gradient = Small resistance.
  • A shallow gradient = Large resistance
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26
Q

Draw a simple circuit which is used to plot a characteristic curve.

A
  • An ammeter and component connected in
    series with a cell.
  • A voltmeter is connected in parallel to the
    component.
27
Q

What is Ohm’s Law?

A

The current through a component is directly proportional to the potential difference across it, as long as the temperature is kept constant.

28
Q

What happens as the potential difference increases across a component?

A

The component gets hotter.

29
Q

What type of circuit element is a wire or fixed resistor?

A
  • A linear circuit element.

- An Ohmic conductor.

30
Q

What does an I-V graph of a wire or fixed resistor show?

A

Resistance is a constant and does not change with potential difference.

31
Q

What type of circuit element is a filament light bulb?

A

A non-linear circuit element.

32
Q

What does the I-V graph of a filament light bulb show?

A
  • Resistance increases with the increasing p.d.

- Resistance increases as the filament gets hotter

33
Q

What is a diode?

A
  • An electrical component that only allows current
    to only flow through one way.
  • Arrow inside points in the direction you want the
    current to flow.
  • Smaller line is connected to the negative terminal
    of the cell/battery.
34
Q

What does an I-V for a diode/LED show?

A
  • Forward resistance is low
  • Reverse resistance is high
  • As you apply a potential difference in the ‘forward’
    direction very little current flows. Then the current
    suddenly increases.”
35
Q

What are thermistors?

A
  • Thermistors are components (resistors) whose
    resistance depends upon temperature.
  • Resistance decreases as the temperature
    increases.
36
Q

Why do thermistors not behave like regular components?

A

Thermistors do not behave like regular components because they are made of a special type of material called semiconductors such as silicon.

37
Q

What happens as you heat up a thermistor/semiconductor or give more light energy to a LDR?

A
  • Ions vibrate faster and fewer electrons move
    through the wire per unit time.
  • More electrons gain enough energy to become
    liberated from the semiconductor which results in
    more electrons moving through the wire per unit
    time.
  • Current increases - Resistance decreases
38
Q

What are LDRs?

A
  • Light dependent resistors are components whose
    resistance depends upon light intensity.
  • Resistance decreases as the light intensity
    increases.
39
Q

What is net resistance and how is it calculated in a series circuit?

A
  • Net resistance is the total resistance of a circuit.
  • Net resistance in a series circuit is calculated by
    summing the individual resistances of all
    components in the circuit.
40
Q

What happens to net resistance in a series and parallel circuit?

A
  • In a series circuit: As you add more resistors,
    the net resistance increases.
  • In a parallel circuit: As you add more resistors,
    net resistance decreases (will always be smaller
    than the smallest resistance of a single branch)
    (current also increases).
41
Q

What is a sensor circuit?

A

A sensor circuit is one which turns on a component on/off automatically, in response to external stimuli.

42
Q

Give an example of thermistors and LDRs in sensor circuits.

A
  • Thermistors are used in sensor circuits in
    thermostats to turn central heating systems
    on/off at desired temperature.
  • LDRs are used in sensor circuits for street
    lamps to turn the lights on/off with changing
    light levels.
43
Q

Describe was happens in a sensor circuit including a thermistor.

A
  • A fixed resistor of resistance R1 is connected in
    series with a thermistor of resistance R2.
  • The p.d. of the battery is shared out amongst the
    fixed resistor and the thermistor - (most p.d. is
    dropped across the resistor with the highest
    resistance).
  • The thermistor is connected in parallel with a
    component like a heater, the potential difference
    across both is Vout.
  • As the temperature in house decreases,
    resistance of thermistor, R2 increases
  • The p.d. dropped across the thermistor Vout
    increases
  • Once Vout increases to a high enough level,
    the “working potential” of the heater is reached
    and it switches on.
44
Q

What is the “ratio trick”?

A

The ratio of resistance of two components is the same as the ratio of the potential difference between the two components.

45
Q

How do you work out the p.d across each component is a series circuit?

A
  • Work out net resistance.
  • Calculate the current in the circuit.
  • Apply V=IR to work out the p.d.
46
Q

What two factors increase the resistance of a wire?

A
  • Increasing the length of the wire.

- Decreasing the thickness of the wire.

47
Q

What is the equation for electrical power in electrical circuits?

A
  • P=IV

- P=I(Squared)R

48
Q

What is electrical power?

A

Electrical power is the rate of electrical energy transfer.

49
Q

Give two properties of a.c. circuits.

A
  • In an a.c. circuit the direction of the current
    changes regularly.
  • In an a.c. circuit the size of the current varies with
    time.
50
Q

What circuit symbol is this?

A

open switch

51
Q

What circuit symbol is this?

A

closed switch

52
Q

What circuit symbol is this?

A

cell

53
Q

What circuit symbol is this?

A

battery

54
Q

What circuit symbol is this?

A

diode

55
Q

What circuit symbol is this?

A

resistor

56
Q

What circuit symbol is this?

A

variable resistor

57
Q

What circuit symbol is this?

A

LED

58
Q

What circuit symbol is this?

A

lamp

59
Q

What circuit symbol is this?

A

fuse

60
Q

What circuit symbol is this?

A

voltmeter

61
Q

What circuit symbol is this?

A

ammeter

62
Q

What circuit symbol is this?

A

thermistor

63
Q

What circuit symbol is this?

A

LDR

LGS GCSE OCR Physics (23 decks)

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