P4,5 ( Circuit Diagram And Component Graph FC's On Paper) & (Coming Up On March Mocks) Flashcards
What is electric current?
The flow of electrical charge.
State the equation linking charge, current and time. Give the units for the quantities involved.
Q =I x 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 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 x 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 or smartphone devices (auto-brightness setting) often use LDRs
● When light levels/screen brightness become too low, the light gains sufficient current to turn on/increase screen brightness
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