Electricity Flashcards
What is electric current?
The flow of electrical charge.
State the equation linking charge
Q = I t
Charge (Coulombs), Current (Amperes),
Time (Seconds)
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 equation should be used to calculate potential
difference if current and resistance are known?
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)
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).
If one lamp blows, the rest will be
unaffected and can still receive current
(i.e. the circuit is still complete)
● 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
Explain when the Earth wire does and doesn’t carry
a current.
● 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
What is the purpose of the neutral wire?
To complete the circuit by connecting the
appliance back to the mains supply.
