Section 5 - Electricity Flashcards
What is a magnet?
Any material or object that produces a magnetic field
What direction do magnetic field lines go?
From north to south
What is induced magnetism?
A temporary magnetic field on a magnetic material that has been induced by a permanent magnet
What is a magnetic material?
Am object that can be influenced by magnetic fields and has the potential to become a magnet
What are some magnetic materials?
Nickel
Cobalt
Iron
What is the difference between magnetically soft and hard materials?
Magnetically soft materials lose their magnetism quicker
What is a battery?
Made up of two or more cells
What is current?
Current is the rate of flow of charge measured in amps
What is current measured by?
An ammeter
What is emf?
The electromotive force is a measure of the electric work done moving each unit of charge round a circuit
What is pd?
Potential difference is the amount of work done by each unit of charge as it passes through a component
What is the formula for pd or emf?
Emf or pd = work/charge
What is the formula for current?
Current = charge / time or I = Q/t
What way round does the current flow in a circuit?
The positive terminal is the longer line of a cell, current flows from the negative to positive terminal.
Although conceptual current is positive to negative
What is resistance?
Resistance is anything in the circuit which slows the flow of charge
What is the equation for resistance?
Resistance = voltage / current Or V = IR
What is the relationship between resistance and the length or cross sectional area of a wire?
Resistance is directly proportionate to is length
Resistance is inversely proportionate to its cross sectional area
How does resistance change in a LDR?
As light gets brighter resistance falls, useful in automatic night lights
How does resistance change in a thermistor?
As it gets hotter resistance drops, useful in car engineer
What does a current-voltage graph show?
How current changes as potential difference is changed
Describe the current-voltage graph of a resistor of constant resistance.
The graph is a straight line through the origin as current is directly proportionate to potential difference - ohms law
What is ohms law?
Ohms law states that current is directly proportionate to potential difference in a fixed resistance resistor when external factors are constant
Describe the current-voltage graph of a filament bulb.
Resistance resistance as current increases because as current increases, temp increases which causes more collisions with the electrons and ions. This increases resistance
Describe the current-voltage graph of a diode.
Diodes only let current though in one direction. They have very high resistance in the reverse direction. So current is zero when pd is negative
What is the formula for electric power and energy transferred?
Electric power (W) = current x potential difference
Energy = current x potential difference x time
Describe current in a series and parallel circuit?
Series - same
Parallel - add to main
Describe pd in series and parallel circuits?
Series - adds
Parallel - same
How to calculate total resistance in parallel?
1/Rt = 1/R1 + 1/R2 + 1/R3
Explain resistance in series and parallel.
Series - add up/ sum of
Parallel - weird calculation
How can you test electric conductors or insulators?
Place in a circuit with a filament lamp
What is an electric field?
An electrified is an area where a force acts on a electric charge
What are the three types of wires in a uk plug?
Live
Neutral
Earth
What can a sudden increase in current or surge or overloading do?
Damage the appliance
Cause fires of electric shocks
What can damp controls do to an electrical circuit?
Can cause electric shock as impure water can conduct electricity
What can overheating cables do to an electrical circuit?
Causes a fire
What can damaged wire insulation do to a circuit?
Lead to live wire being exposed. Could cause shock
What is the usual voltage from a ac supply?
230V
What is the use of a fuse and why do they come in different ratings?
Contains a thin piece of wire that melts when the current gets too high to break the circuit. Different ratings are used depending on what current you want to break the circuit.
What is a circuit breaker?
Circuit breakers or trip switches are similar to fuses in that break the circuit,
They do this by opening or tripping which means they don’t need to be replaced every time they trip
What is the importance of double casing or earthing?
When a surge causes a wire to touch a metal case it may cause a shock.
Double casing or earthing prevents this
What is double casing?
Double casing is a plastic casing that goes over an Epstein appliance to stop electric shocks. Appliances that are double cased do not need an earth wire.
