Electricity Flashcards
We buy electrical energy in units called
Kilowatt hours (kWh)
1kW = ? W
1000
1kW charged by Eskom =
R1,70
Paying for electricity formula
Cost = power x time x rate
Source of the electric current
Electrical cells
In a cell -
Chemical energy is converted into electrical energy
Series circuit only provides
One pathway for the charge to move
Charge:
1. Unit
2. Symbol
- Coulomb (C)
- Q
Current:
1. Unit
2. Symbol
- Amperes (A)
- I
Time:
1. Unit
2. Symbol
- Seconds (s)
- t
Resistance:
1. Unit
2. Symbol
- Ohms (Ω)
- R
Potential Difference:
1. Unit
2. Symbol
- Volts (V)
- Voltage (V)
Effects of an electric current
- Heating effect
- Magnetic effect
- Chemical effect
Magnetic effect
- When an electric current flows in a conducting wire, a magnetic field develops in the space around the conductor
- Magnetic field is in the form of concentric circles around the conductor
Series Circuit current
A1 = A2 = A3
Parallel Circuit current
A1 = total current
A1 = A2 + A3
Current formula
Current = charge moved ÷ time taken
I = Q ÷ t
When a cell is in a complete circuit …
The chemicals (chemical energy) react with each other
The charge are given _________ energy they need to ______
Potential
Start moving through the circuit
When a charge receives more energy
It releases more energy
Why is a voltmeter connected in parallel?
Because it measures potential difference across the ends of a cell/resistor (light bulb)
Why is an ammeter connected in series?
So that all the current flows through the ammeter and can be measured
Voltmeter connected in ….
Parallel
Ammeter connected in ….
Series
Voltmeter has ________ resistance because
Very high
It forces current to flow through the cell/lightbulb not through the voltmeter
Ammeter has _______ resistance because
Low
It allows the current to flow through the ammeter so that it can measure it
Work done =
Energy transferred
1 Volt =
1 J per Coulomb
Ohmic Resistor
- The graph for V against I is a straight line that goes through the origin
- Relationship between current and potential difference is directly proportional
Non-Ohmic resistor
- The graph for V against I is not a straight line
Resistance formula
Resistance = potential difference ÷current
R = V ÷ I
State Ohm’s Law
Current through a conductor is directly proportional to the potential difference across the conductor at constant temperature
Factors that affect resistance
- Type of material
- Length of conductor
- Thickness of conductor
- Temperature of material
Type of metal used
Different conducting materials have different resistances
Length of conductor
- More length = more resistance
- Less length = less resistance
- Resistance is directly proportional to the length of metal conductor
Thickness of conductor
- Thinner conductor = more resistance
- Thicker conductor = less resistance
- Resistance is inversely proportional to the thickness of metal conductor
- Inversely proportional graph = hyperbola
Temperature of conductor
- Hotter conductors = more resistance
- Cooler conductors = less resistance
Potential Difference in Series
The sum of potential difference across each individual resistor is equal to the potential difference across the battery
Potential Difference in Parallel
The potential difference across each resistor in parallel is equal to each other and equal to the potential difference across the battery
Resistors in series are called
Potential dividers
Resistors in parallel are called
Current dividers
Kilowatt hour is another
Unit for energy