Direct current (DC) flows in one direction only. Cells, batteris and solar cells are DC.
Electrons always from from + to -.
Alternating current oscillates (reverses its direction) continuously.
50 herts means it oscillates 50 times per second.
Cells and batteries are sources of direct current.
Wet cell rechargeable- contains lead and acid and is used for cars and industry.
Dry cell non-rechargeable contains zinc, carbon, maganese, or mercury, lithium and is used for torches, clock, radios, hearing aids, pacemakers.
Dry cell rechargeable contains nikel, cadmium, lithium and it used for mobile phones and powere tools.
Non-rechargeable batteries are not benefical to the environment because they need a high amount of energy , less than 5% is recycled, toxic chemicals can leak into the ground causing pollution.
However, rechargeable batteries are less expensive in the long run, can be reused, fewer battries are discarded into the environment, less of a drain of energy resources.
A charger must be purchased, more expenisve, most contain cancer causing chemicals, can go flat without warning.
The capacity of a battery is a measure of how much energy it can store. It is measured in amps-hour (Ah)
Solar cells are also a source of electrical energy. They produce a direct current using the Sun's light energy.
Electric current needs a complese circuit to flow.
Current is the rate of flow of electrons in a component.
Electrons have a negative charge.
In a complete circuit they leave the negative terminal because they are attracted to the positive.
The greater the flow of electrons the greater the current.
When current is flowing, energy is transferred from the cell to the circuit components (devices).
If the component has a voltage the electric current will flow through it.
The atoms of all materials contain electrons but they are normally strongly bound by attraction to the positive nucleus of the atom.
When a conductor is connected to a DC supply, the voltage (potential difference) drives the electrons along the conductor. This is an electric current.
The greater the potential difference, the greater the electron flow and the greater the current.
Current (the measure of electron flow) is measured using a ammeter in units called amperes (amps A)
Voltage (measure of electrical force) is measured in volts using a voltmeter (must be connected across a component
Current and voltage can be measured at the same time.
If you move a wire so that it cuts through a magnetic field, then a voltage is induced between the ends of the wire.
This will cause electrons to flow along the wire creating an electric current, if the wire is part of a complete circuit.
The same effect can be seen using a coil and a magnet.
To increase the voltage; have stronger magnets, have more coils of wire, move the wire faster.
Generators-use the principle of moving coils of wire in a magnetic field to generate electricity
...is the measure of how hard it is for a current to flow through a conductor. It is measured in ohms.
For most materials resistance increases in proportion to an increase in temperature.
Thermistors- work in the oppisite way:they are inversley proportional. Their resistance decreases at the temperature increases.
A resistor is a component which has a fixed resistance. When an electric current passes through a resistor, the moving electrons collde with atoms within the resistor, giving up their energy, resulting in an temperature increase.
Light dependant resistors and thermistors are components who resistance depends on the surrounding external conditions.
The resistance of an LDR decreases as the light intensity increases.
The resistance of a thermistor decreases as the temperature increases.
Insulators have resistances which are so large that, under normal circumstances, current cannot flow.
As more components are added into a series circuit the resistance increases.
However, it is not true for a parrallel circuit.
A variable resistor- is a component whose resistance can be altered- by doing this the current can change which flows through a component aswell as the voltage.
...show how the current through a component varies with the voltage across it. If we include a variable resistor in our circuit, we can get a range of current and voltage readings, needed to plot a graph.
Electrcity has had a huge impact on the world.
superconductivity- materials that cool on a certain temperature with zero resistance. (currently it is only carried out at low temperatures.)
Maglev train- was based on superconductvity. Maglev trains were moved along by electromagnets.