Chapter 4 and 5 Science Revision (Current and charge (Electon Flow (Charge…
Chapter 4 and 5 Science Revision
Electrical currents and energy transfer
Chemical energy stored in the cell/batery
Electrical energy in the circuit (kinetic energy on the electrons)
CHARGE FLOW X VOLTAGE
Kinetic energy of the ions in the resistor (e.g. a bulb)
Store of thermal energy in the resistor increases
Electrical power and Potential difference
POWER - The power rating of an appliance is simply how much energy it uses every second
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
POWER = ENERGY / TIME
POWER = CURRENT(2) x RESISTANCE
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
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
For components in series
The current is the same in each component
Adding their resistances go to the total resistance
The total potential difference is shared between the components
Potential difference and Resistance
Current voltage graphs
VOLTAGE = CURRENT x RESISTANCE
Voltage is measured in Volts (V)
Resistance is measured in Ohms
Current is measured in Amps (A)
The steeper the gradient of a current voltage graph, the lower the resistance of the wire
When voltage is doubled, current also doubles. When voltage is tripled, current also triples.
This means they are directly proportional
Plotting current against voltage produces a straight line
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.
In metals with low resistance, fewer collisions occur and the current can flow more easily
More collisions occur and electrical energy is wasted as light and heat. The current decreases and the metal gets hotter
If a metal has fewer free electrons = high resistance. Fewer electrons are available to carry charge, so current is reduced
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
Current and charge
Charge is carried by electrons, flowing from the negative terminal to the positive terminal.
The idea of positively charged particles from the positive terminal around a circuit to the negative terminal
Charge flow (Q) = Current (I) x Time (t)
Electric charge is measured in coulombs
Current is the rate of flow of electric charge in a circuit.
Electrical charges and fields
What is static electricity?
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
How can static charge be created?
Friction can be used to create a static charge through electron transfer
Static electricity is due to the build up of electric charge on the surface of an insulator