Electricity Flashcards
A power of 1 watt is equivalent to what?
1 joule per second (1 J/s)
A current of 1 amp is equivalent to what?
1 coulomb per second (1 C/s)
A voltage of 1 volt is equivalent to what?
1 joule per coulomb (1 J/C)
What are current and voltage like in parallel circuits?
1) voltage is the same across each branch
2) current splits up between branches
What are current and voltage like in series circuits?
1) voltage splits up between the individual components
2) current is the same everywhere on the circuit
What is an advantage of connecting two heating elements in series?
Single switch to control both
What is an advantage of connecting two heating elements in parallel?
1) Independent control as components can all be switched on and off separately
2) other components stay alight if one component blows
Describe how an earth wire acts as a safety feature
1) earth wire connected to metal casing
2) if casing becomes live
3) provides low resistance path to earth
4) so large current in earth wire
5) hence fuse breaks
6) so circuit switches off as incomplete
Why should components with a metal casing be earthed?
1) metal case
2) metal conducts electricity
3) to prevent user getting a shock
Explain why the resistance of a filament lamp changes as the voltage is increased
1) lamp heats up
2) greater chance of electron collisions
3) hence resistance increases
How do fuses act as a safety feature?
If the current gets too high the fuse melts breaking the circuit
Which non-metal can conduct electricity?
Carbon
What is the current in a metallic conductor?
A flow of negatively charged electrons
Describe the circuit uses to measure the resistance of a component
1) component, power supply and ammeter in series
2) voltmeter in parallel across the component
How does the resistance change as the voltage increases in a diode?
The resistance drops as the voltage increases (no current if voltage is below 0.6 - including negative values)
What is Ohm’s law?
The resistance of a metal wire at a constant temperature does not change as the voltage across it is varied, meaning the current is PROPORTIONAL to the voltage.
What is a light dependent resister (LDR)?
A component whose resistance drops as the brightness of the light falling on it increases (as charge carriers are released when energy falls on the material)
What is a thermistor?
A component who’s resistance drops as temperature increases
What is meant by the term 5A fuse?
A thin wire which melts at an excess of 5 amps breaking the circuit
Give two advantages of using a circuit breaker as opposed to a fuse
1) can be reset so doesn’t need to be replaced
2) work instantly unlike fuses
What is meant by the term earthed?
1) outside case made of metal
2) connection to ground
Why might a data-logger be preferable to a voltmeter?
Take readings at a greater frequency
What is meant by an alternating current?
1) current changing direction
2) continuously
If a lamp Y gives the same amount of light but uses much less power than lamp X, what is true of the voltage and current?
1) voltage is same in X and Y
2) current is lower in Y than in X
Why is water a hazard around electricity?
It conducts electricity causing a short circuit
Why does damaged electrical equipment cause a hazard?
Live parts might be exposed causing a shock
Why do trailing cables present a hazard?
Trip hazard
What is the purpose of a fuse?
To prevent overheating in a circuit by switching off the circuit and hence preventing current exceeding a certain value
How is the value of a fuse decided?
Fuse value should only be a little bigger than the current
What colour is the live wire and where is it located in a plug socket?
Brown and on the right
What colour is the neutral wire and where is it located in a plug socket?
Blue and on the left
What colour is the earth wire and where is it located in a plug?
Green and yellow and at the top
What kind of current is mains electricity?
Alternating current
What current do batteries supply?
Direct current
Which way does conventional current flow?
Positive to negative
Describe how the resistance in a wire at a constant temperature changes as the voltage is increased
Does not change (therefore current and p.d are directly proportional on a graph)
Describe how the resistance in a filament bulb changes as the voltage is increased
Resistance increases as voltage is increased due to temperature increase so more electron collisions occur (therefore current increases quickly then slowly on graph as voltage increases)
What is a resistor?
A component designed to control the current flowing in a circuit
What is voltage?
The energy transferred per unit charge passed
What is current?
The charge passing a fixed point every second
What is resistance?
A measure of how much a material inhibits the current flowing through it
Which wire is the fuse connected to?
The live wire
Why can a build up of charge be dangerous?
Possibility of a spark or explosion
How can a build up of electrostatic charge be prevented?
Earth the appliance
How do materials gain a positive or negative electrostatic charge?
By the gain or loss of electrons (NOT PROTONS)
What kind of materials can be charged by friction?
Insulating materials (with conducting materials any charges that are produced are quickly conducted away)
How are electrostatic charges used in photocopiers and laser printers?
1) a rotating drum coated with a layer of photoconductive material is given a uniform charge
2) a light/laser beam then ‘draws’ an image of the object to be copied/printed onto the drum
3) the electrostatic charge drains away form the exposed areas
4) black toner powder is then allowed to stick to the remaining charges areas
5) the drum transfers the toner to a piece of paper and the two are fused together by heat
How is electrostatic charge used in electrostatic precipitation?
This is a method of removing small particles from exhaust gases from factories:
1) particles given an electrostatic charge as they enter the chamber
2) the particles are attracted to the electrodes carrying the opposite charge
3) electrodes stripped of the particles every so often
How do objects gain an electrostatic charge?
Transfer of electrons due to friction
Explain why a man could receive a shock even if a metal appliance is properly earthed?
1) metal is a conductor to earth
2) there is a voltage between the man and the button
3) transfer of electrons
4) current in man’s body
explain what happens when a cloud discharges
1) electrons move
2) to earth
3) air conducts
4) lightning
if an LED is on, it shows what?
that there is a current/voltage in the circuit
using a high voltage does what to the efficiency of the transmission?
increases the efficiency of the transmission
explain how an object becomes charged by friction
1) rubbing of materials/surfaces
2) movement/transfer of electrons
3) electrons have a negative charge;
4) object becomes negatively charged by gaining electrons positively charged by losing electrons
5) need for insulating materials
explain why electrical energy is transmitted at very high voltages
1) High voltage leads to low current;
2) mention of a relevant equation e.g. P = I^2 x V
3) Less energy is lost from the wires
4) More efficient
5) can use thinner wires
A kettle is earthed and fitted with a fuse. Explain how this can protect the person using the kettle if there is a fault.
1) large current in earth wire
2) fuse melts/blows
3) circuit is broken
4) risk of shock is reduced
