Chapter 4 Flashcards
Electricity and magnetism
What is alternating current (a.c.)?
The direction of current flow reverses repeatedly
What is direct current (d.c.)?
Electrons flow in one direction only
Define electric current
The charge passing a point per unit time [current I = Q/t where Q is the charge flowing past a particular point in time t]
What is an electromagnet?
Temporary magnet produced by passing an electric current through a coil of wire wound on a soft iron core
Explain electromagnetic induction
The production of a p.d. across a conductor when it moves through a magnetic field or is at rest in a changing magnetic field
What is electromotive force (e.m.f.)?
The electrical work done by a source in moving unit charge round a complete circuit
What is a kilowatt-hour (kWh)?
The electrical energy transferred by a 1 kW appliance in 1 hour
Define light-dependent resistor (LDR)
Semiconductor device in which the electrical resistance decreases when the intensity of light falling on it increases
What is a magnetic field?
A region of space where a magnet experiences a force due to other magnets or an electric current
What are magnetic materials?
Materials that can be magnetised by a magnet; in their non-magnetised state, they are attracted by a magnet
What are non-magnetic materials?
Materials that cannot be magnetised and are not attracted to a magnet
Describe a parallel circuit
Components connected side by side and the current splits into alternative paths and then recombines; current from the source is larger than the current in each branch
What is a permanent magnet?
Made of steel and retains its magnetism
Define potential difference (p.d.)
The work done by a unit charge passing through a component
What is a relay?
Electromagnetic switch
What is resistance?
Opposition of a conductor to the flow of electric current; symbol R measured in ohms (Ω)
Describe a series circuit
Components connected one after the other; the current is the same in each part of a series circuit
What is a solenoid?
Long cylindrical coil of wire
Define a temporary magnet
Made of soft iron, and loses its magnetism easily
What is a thermistor?
Semiconductor device in which the electrical resistance decreases when the temperature increases
What is a transformer?
Two coils (primary and secondary) wound on a soft iron core which allow an alternating p.d. to be changed from one value to another
What is conventional current?
Flows from positive to negative; the flow of free electrons is from negative to positive
Define an electric field
A region in space where an electric charge experiences a force due to other charges
What is a light-emitting diode (LED)?
Semiconductor device which emits light when it is forward biased but not when it is reverse biased
What is a potential divider?
Provides a voltage that varies with the values of two resistors in series in a circuit
