Chapter 4 and 5 Science Revision (Current and charge (Conventional Current…
Chapter 4 and 5 Science Revision
Electrical charges and fields
What is static electricity?
Static electricity is due to the build up of electric charge on the surface of an insulator
How can static charge be created?
Friction can be used to create a static charge through electron transfer
If two rods of the same material are rubbed with the same type of cloth, they gain the same type of charge, meaning that they repel
Two rods of different material are attracted to each other as they both have opposite charges
Current and charge
Current is the rate of flow of electric charge in a circuit.
Electric charge is measured in coulombs
Charge flow (Q) = Current (I) x Time (t)
The idea of positively charged particles from the positive terminal around a circuit to the negative terminal
Charge is carried by electrons, flowing from the negative terminal to the positive terminal.
Potential difference and Resistance
Potential difference is a measure of the difference in electrical potential energy between two points in a circuit. Potential difference is also called Voltage
Voltage is measured in volts (v) using a Voltmeter
The voltage of a battery of a cell is a measure of the force or "push" it gives the current.
Potential difference = Energy transferred / Charge
What affects the size of the current?
Current is a measure of the rate of flow electric charge through a circuit. A large current means that the rate of flow is more rapid. Current can be changed by increasing or decreasing the voltage of the current.
Components in a circuit may reduce the size of the current. This is called resistance. All wires and components resist current
Resistance is a measure of how hard it is for electrons to move in an electrical circuit.
If a metal has fewer free electrons = high resistance. Fewer electrons are available to carry charge, so current is reduced
More collisions occur and electrical energy is wasted as light and heat. The current decreases and the metal gets hotter
In metals with low resistance, fewer collisions occur and the current can flow more easily
Current voltage graphs
Plotting current against voltage produces a straight line
This means they are directly proportional
When voltage is doubled, current also doubles. When voltage is tripled, current also triples.
The steeper the gradient of a current voltage graph, the lower the resistance of the wire
VOLTAGE = CURRENT x RESISTANCE
Current is measured in Amps (A)
Resistance is measured in Ohms
Voltage is measured in Volts (V)
For components in series
The total potential difference is shared between the components
Adding their resistances go to the total resistance
The current is the same in each component
For cells in series, acting in the same direction, the total potential difference is the sum of their individual potential differences.
Total resistance = Rtotal = R1, + R2
Adding more resistors in series increases the total resistance because the current through the resistors is reduced and the total potential difference across them is unchanged
Electrical power and Potential difference
POWER - The power rating of an appliance is simply how much energy it uses every second
POWER = ENERGY / TIME
POWER = CURRENT(2) x RESISTANCE
Power is "the rate of doing work". The amount of power being used in an electrical circuit is gained by
POWER = POTENTIAL DIFFERENCE x CURRENT
Electrical currents and energy transfer
Chemical energy stored in the cell/batery
Electrical energy in the circuit (kinetic energy on the electrons)
Kinetic energy of the ions in the resistor (e.g. a bulb)
Store of thermal energy in the resistor increases
CHARGE FLOW X VOLTAGE