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Physics > Unit 2 - Electricity > Flashcards

Unit 2 - Electricity Flashcards

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1
Q

What can be said about the value of current at any
point in a single closed loop?

A

Current is the same at all points in a
closed loop.

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2
Q

What two factors does the current in a circuit depend
on?

A
  1. Potential Difference (V)
  2. Resistance (R)
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3
Q

What equation should be used to calculate potential
difference if current and resistance are known? State
the units for all 3 quantities.

A

V = I R
Potential Difference (V), Current (A),
Resistance (Ω)

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4
Q

What is an ‘Ohmic Conductor’? State the condition
required.

A

● A conductor for which current and potential
difference are directly proportional
● Resistance remains constant as current
changes
● Temperature must be constant

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5
Q

List four components for which resistance is not
constant as current changes.

A
  1. Lamps
  2. Diodes
  3. Thermistors
  4. Light Dependant Resistors (LDRs)
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6
Q

What happens to the resistance of a filament lamp
as the temperature increases? Why?

A

● Resistance increases
● Ions in metal have more energy, so vibrate
more, causing more collisions with
electrons as they flow through the metal,
creating greater resistance to current flow

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7
Q

What is different about current flow
through a diode?

A

● The current only flows in one direction
● Resistance is very high in the other
direction, preventing current flow

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8
Q

State what happens to the resistance of a thermistor
as temperature increases.

A

The thermistor’s resistance decreases.

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9
Q

Give two examples of when a thermistor may be
used.

A
  1. In a thermostat to turn a heater on
    below a certain temperature
  2. In a freezer to turn on a cooler when
    the temperature becomes too high
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10
Q

State what happens to the resistance of a LDR as
light intensity decreases.

A

The LDR’s resistance increases.

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11
Q

Give an application for a LDR.

A

● Street lights often use LDRs
● When light levels become too low, the
light gains sufficient current to turn on

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12
Q

What are the two ways that a component can be
connected in a circuit?

A
  1. Series (same loop)
  2. Parallel (adjacent loop)
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13
Q

How does the potential difference across two
components vary when connected in series and
parallel?

A

● Series: Total P.D is shared between
each component
● Parallel: P.D across each component
is the same

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14
Q

If two resistors are connected in parallel, what can
be said about their combined total resistance?

A

Their total resistance is less than the
smallest of the two individual
resistances.

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15
Q

If two resistors are connected in series, what can be
said about their total resistance?

A

Their total combined resistance is equal
to the sum of the two individual
resistances.

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16
Q

Describe the current in a series circuit

A

In a series circuit, the current is the same
at all positions since the charge only has
one path to flow through.

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17
Q

Describe the current in a parallel circuit.

A

In a parallel circuit, the current is shared
between the different branches. When
the charge reaches a junction it splits.

18
Q

How should you connect an ammeter in a circuit to
measure current?

A

Ammeters should be connected in series
with the component that they are
measuring current through.

19
Q

How should you connect a voltmeter in a circuit to
measure potential difference?

A

Voltmeters should be connected in
parallel to the component that they are
measuring the potential difference of.

20
Q

Why is it advantageous to connect lamps in parallel?

A

If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete).

21
Q

Is mains electricity an a.c supply or a d.c supply?
What do each of these stand for?

A

Mains electricity is an a.c supply
a.c. : Alternating Current
d.c. : Direct Current

22
Q

Define alternating current and direct current.

A

● Alternating current: Current that
continuously changes direction at a
specific frequency
● Direct current: One directional current
flow

23
Q

What is the frequency and voltage of the UK mains
electricity supply?

A

● Frequency: 50 Hz
● Voltage: 230V

24
Q

How many wires are usually in the cables connecting
electrical appliances to the mains? Name these
wires.

A
  1. Live wire
  2. Neutral wire
  3. Earth wire
25
Q

State the insulation colour used on the Earth wire.

A

Green and Yellow Stripes

26
Q

State the insulation colour used on the live wire.

A

Brown

27
Q

State the insulation colour used on the Earth wire.

A

Blue

28
Q

Explain when the Earth wire does and doesn’t carry
a current.

A

● Under normal circumstances, no current
flows through the Earth wire
● If a fault occurs in the appliance (such as a
surge or the casing becoming live), current
will flow to the ground

29
Q

What potential is the neutral wire at?

A

0 Volts

30
Q

State the potential difference between the live and
earth wires.

A

230 Volts

31
Q

What is the purpose of the neutral wire?

A

To complete the circuit by connecting the
appliance back to the mains supply.

32
Q

For metal appliances, where is the Earth wire
connected to? Why?

A

● Earth wire is connected to the metal casing
of the appliance
● If live wire becomes loose and touches the
casing, the current will flow through the
Earth wire, preventing electrocution

33
Q

What two main factors does the amount of energy
transferred by an appliance depend on?

A
  1. How long the appliance is being used
    for
  2. The power of the appliance
34
Q

Describe the energy transfers in a battery powered
torch.

A

● Battery converts chemical energy into
electrical energy
● Bulb converts electrical energy into light
as well as waste energy in the form of
heating

35
Q

Describe the energy transfers in a battery powered
motor.

A

● Battery converts chemical energy into
electrical energy
● Motor converts electrical energy into
kinetic energy as well as waste energy
in the form of heating due to friction

36
Q

What three things determine the power of a circuit
device?

A
  1. The potential difference across the
    circuit
  2. The current through the circuit
  3. The amount of energy transferred in a
    given time
37
Q

What is the purpose of the National Grid?

A

To link power stations to consumers so
that they have access to a source of
electricity.

38
Q

What are the two types of transformers used in the
National Grid?

A
  1. Step-Up Transformers
  2. Step-Down Transformers
39
Q

Where are step-up transformers found in the
National Grid? What do they do?

A

● Step-Up Transformers are used when
connecting power stations to
transmission cables
● They increase the potential difference

40
Q

Where are step-down transformers found in the
National Grid? What do they do?

A

● Step-Down Transformers are used in
connecting transmission cables to
domestic buildings (like houses)
● They decrease the potential difference

41
Q

Why do transmission lines transfer electricity at high
potentials?

A

● A high potential, results in a low current
● The lower the current, the less energy
that is wasted as heat
● Therefore it is more efficient

42
Q

Why does the potential need to be decreased
between transmission lines and houses?

A

● Lower potentials are safer for domestic
use and reduces the likelihood of
severe electrocution
● Appliances are designed for 230V

Physics (7 decks)

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