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gcse physics > electricity > Flashcards

electricity Flashcards

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1
Q

switch

A
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2
Q

cell / battery

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3
Q

resistor

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4
Q

diode

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5
Q

LED - light emmitting diode

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6
Q

lamp

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7
Q

fuse

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8
Q

voltmeter

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9
Q

ammeter

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10
Q

thermistor

A
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11
Q

LDR - Light dependent resistor

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12
Q

ohmic conductor

A

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.

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13
Q

non ohmic conductors

A

The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.

This is because as the potential difference across the bulb increases, the current through the bulb increases.
As the current increases the
temperature increases.
As the temperature increases, the resistance increases.

We can tell that lamps and diodes are not ohmic conductors because their I-V graphs are non- linear (i.e. I & V cannot be directly proportional)

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14
Q

diode current

A

The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction and only conducts over a certain threshold po
tential.

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15
Q

thermistor resistance

A

The resistance of a thermistor decreases as the temperature increases. This makes them useful in devices such as thermostats.

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16
Q

LDR resistance

A

The resistance of an LDR decreases as light intensity increases. They are used in sensing circuits that can be used to automatically turn lights on when it gets dark.

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17
Q

current

A

An electric current is a flow of electric charge. For electric charge to flow through a closed circuit the circuit must include a source of potential difference.
The size of the electric current is the rate of flow of charge

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18
Q

the equation for electric current

A

Q=It
Charge (coulomb / C) = Current (amp / A) x time (seconds / s)

I = Q/T
amps = number of coulombs that pass a point every second
ie. 3 amps = 3 coulombs passing a point every second

19
Q

Show how an ammeter is used to measure the current through a lamp

A
20
Q

potential difference

A

The potential difference across a component is a measure of how much energy is transferred by each unit of charge that passes through the component

21
Q

equation for potential difference

A

E=QV
energy transferred (J) = Charge (Coulombs / C) x potential difference (volts / V)

V = E/Q
volts = Joules per coulomb
ie. 10 volts = 10 Joules per coulomb

22
Q

Show how a voltmeter is used to measure the p.d. across a lamp

A
23
Q

resistance

A

As electrons flow through a conductor they collide with metal ions: the flow of current is being resisted. The resistance of a component is measured in ohms (Ω).

24
Q

equation

A

V=IR
potential difference (Volts / V) = current (Amps / A) x resistance (ohms / Ω)

25
Q

Draw a circuit diagram that would enable the resistance of a resistor to be determined:

A
26
Q

For components connected in series:

A
  • The current through components connected in series is the same at all pomts
  • The total potential difference of the power supply is shared between the components
  • The total resistance is the sum of the resistance of each component

Adding another resistor in series will increase the total resistance in the circuit and descrease the total current in the circuit. The total resistance of resistors connected in series is the sum of individual resistors.

27
Q

For components connected in parallel:

A
  • the potential difference across each component is the same (not split!)
  • the total current through the whole circuit is the sum of the
    currents through the separate components
  • the total resistance of two resistors is less than the resistance of
    the smallest individual resistor

Adding another resistor in parallel will decrease the total resistance in the circuit and increases the total current in the circuit. The total, or equivalent, resistance of identical resistors connected in parallel, is calculated using:
Resistance of 1 resistor / number of resistors

28
Q

alternating current (ac)

A

An alternating current (ac) is where the charges continuously change direction. The terminals alternate between being positively an negatively charged.

Mains electricity is an AC supply. In the United Kingdom the domestic electricity supply has a frequency of 50 Hz and is about 230V.

29
Q

direct current (dc)

A

A direct current (dc) flows in one direction only and by convention flows from positive to negative. (Although the electrons flow from negative to postive!)

30
Q

role of each wire in AC

A

The role of each wire is as follows:

The live wire carries the alternating potential difference from the supply.

The neutral wire completes the circuit.

The earth wire is a safety wire to stop the appliance becoming live.

The potential difference between the live wire and earth (0 V) is about 230 V.
The neutral wire is at, or close to, 0V
The earth wire is at 0V, it only carries a current if there is a fault.

31
Q

three pin plug

A
32
Q

Why is it very dangerous for anyone standing on the ground to touch a live wire?

A

The live wire has a potential of 230V and the Earth has a potential of 0 V. There is now a potential difference of 230V across the person touching the live wire. This will cause a current to flow through them, causing an electric shock.

33
Q

The National Grid

A

The National Grid is a system of cables and transformers linking power stations to consumers.

34
Q

Step-up transformers

A

Step-up transformers are used to increase the potential difference from the power station to the transmission cables.

35
Q

Step-down transformers

A

Step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.

36
Q

transformers

A

Transformers make the transfer of energy more efficient because increasing the p.d. decreases the current flowing through the power cables. This reduces the energy wasted as heat. The equation P=I2R shows that less power is wasted as the current decreases.

37
Q

Power

A

Power is defined as the rate at which energy is transferred

38
Q

power transfer

A

The power transfer in any circuit device is related to the potential difference across it and the current through it.
P=IV
power (watts W) = current (Amps / A) x potential difference (volts / v)

39
Q

electrical power

A

Electrical power can also be related to the current through a component and the resistance of the component.
P=I2R
power (watts W) = current (Amps / A)^2 x resistance

40
Q

Draw a circuit that would allow you to investigate how the
resistance of a resistance wire changes with length.

A
41
Q

Draw a circuit that would allow you to investigate the current p.d. graph
filament bulb.

A
42
Q

potential divider circuit

A

A potential divider circuit is a simple circuit where two components are connected in series. In a Potential divider the circuit ratio of p.d. across the components is equal to the ratio of resistances.

43
Q

Using a variable resistor, thermistor or LDR as one of the
components in a potential divider circuit.

A

As the light level increases, the resistance of the LDR decreases.
the total resistance of the circuit decreases so the current in the circuit increases.
The fixed resistor is now a greater proportion of the total resistance, so the p.d. across the fixed resistor increases and the p.d. across the LDR decreases

gcse physics (8 decks)

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