Unit 2 - Electricity Flashcards
(42 cards)
What can be said about the value of current at any
point in a single closed loop?
Current is the same at all points in a
closed loop.
What two factors does the current in a circuit depend
on?
- Potential Difference (V)
- Resistance (R)
What equation should be used to calculate potential
difference if current and resistance are known? State
the units for all 3 quantities.
V = I R
Potential Difference (V), Current (A),
Resistance (Ω)
What is an ‘Ohmic Conductor’? State the condition
required.
● A conductor for which current and potential
difference are directly proportional
● Resistance remains constant as current
changes
● Temperature must be constant
List four components for which resistance is not
constant as current changes.
- Lamps
- Diodes
- Thermistors
- Light Dependant Resistors (LDRs)
What happens to the resistance of a filament lamp
as the temperature increases? Why?
● 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
What is different about current flow
through a diode?
● The current only flows in one direction
● Resistance is very high in the other
direction, preventing current flow
State what happens to the resistance of a thermistor
as temperature increases.
The thermistor’s resistance decreases.
Give two examples of when a thermistor may be
used.
- In a thermostat to turn a heater on
below a certain temperature - In a freezer to turn on a cooler when
the temperature becomes too high
State what happens to the resistance of a LDR as
light intensity decreases.
The LDR’s resistance increases.
Give an application for a LDR.
● Street lights often use LDRs
● When light levels become too low, the
light gains sufficient current to turn on
What are the two ways that a component can be
connected in a circuit?
- Series (same loop)
- Parallel (adjacent loop)
How does the potential difference across two
components vary when connected in series and
parallel?
● Series: Total P.D is shared between
each component
● Parallel: P.D across each component
is the same
If two resistors are connected in parallel, what can
be said about their combined total resistance?
Their total resistance is less than the
smallest of the two individual
resistances.
If two resistors are connected in series, what can be
said about their total resistance?
Their total combined resistance is equal
to the sum of the two individual
resistances.
Describe the current in a series circuit
In a series circuit, the current is the same
at all positions since the charge only has
one path to flow through.
Describe the current in a parallel circuit.
In a parallel circuit, the current is shared
between the different branches. When
the charge reaches a junction it splits.
How should you connect an ammeter in a circuit to
measure current?
Ammeters should be connected in series
with the component that they are
measuring current through.
How should you connect a voltmeter in a circuit to
measure potential difference?
Voltmeters should be connected in
parallel to the component that they are
measuring the potential difference of.
Why is it advantageous to connect lamps in parallel?
If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete).
Is mains electricity an a.c supply or a d.c supply?
What do each of these stand for?
Mains electricity is an a.c supply
a.c. : Alternating Current
d.c. : Direct Current
Define alternating current and direct current.
● Alternating current: Current that
continuously changes direction at a
specific frequency
● Direct current: One directional current
flow
What is the frequency and voltage of the UK mains
electricity supply?
● Frequency: 50 Hz
● Voltage: 230V
How many wires are usually in the cables connecting
electrical appliances to the mains? Name these
wires.
- Live wire
- Neutral wire
- Earth wire
