Phy2 - Electricity Flashcards
What is current?
The rate of flow of charge
What is the equation for charge flow?
Charge flow = current × time
Q = I × t
What is the equation for potential difference?
Potential Difference = current × resistance
V = I × R
For a given potential difference
what happens to the current when the resistance increases?
The current decreases
What happens to the resistance of a thermistor as temperature increases?
The resistance decreases
What happenes to the resistance of a LDR as light increases?
Resistance decreases
What is the diifference between direct current and alternating current?
• Direct current flows in only one direction
• Alternating current constantly changes direction
What is the rule for current in a series circuit?
Current stays the same througout the whole circuit
Name the electrical component in thermostats
Thermistor
Where are LDRs commonly found?
LDRs are used as automatic night
lights / burglar detectors (in bright light the resistance is low)
What is the National Grid?
A system of cables and transformers
What is the rule for potential difference in series circuits?
Potential difference is shared between components
Where should you place an ammeter to measure the current through a component?
The ammeter should be placed in series with the component
What is the rule for potential difference in a parallel circuit?
It stays the same in each branch
Where should you place a voltmeter to measure the potential difference through a component
The voltmeter should be placed parallel to the component
What type of electricity supply is a battery?
Direct current (DC)
What is the total resistance of these resistors in series?
—[]——[]——[]—
10Ω 10Ω 5Ω
25Ω
What is the rule for current in a parallel circuit?
Current is shared between the branches
What type of electricity supply is mains electricity?
Alternating current (AC)
Name the piece of equipment used to measure potential difference
Voltmeter
What is the frequency of mains electricity?
50 Hz
Name the 3 wires in a 3-core cable and say what colour they are
• Live wire (brown)
• Neutral wire (blue)
• Earth wire (green /yellow
striped)
What is the function of the neutral wire (blue)?
Completes the circuit carrying current away (0V)
What is the function of the live wire (brown)?
Provides the alternating potential difference (230V)
What is the function of the earth wire (yellow/green)?
Acts as a safety device, stopping the appliance casing from becoming live (0V)
What is the equation of power, current and potential difference?
Power = Current × PD
Power = I × V
What two things determine the energy transferred from an electrical appliance?
• How long the appliance is on for
• The power rating of the appliance
What is the equation for energy transferred?
Energy transferred = Charge flow × potential difference
E = Q × V
What is the equation for power, current and resistance?
Power = current² × resistance
P = I² × Ω
What is the potential difference of Mains Electricity?
230V
In a parallel circuit, what happens to the total resistance when you add a resistor?
The total resistance decreases
What is the equation for energy transferred, power and time?
Energy transferred = Power × time
E = P × t
What piece of equipment is used to measure current?
Ammeter
