P2-Electricity Flashcards
What is static electricity?
Electric charge stored on insulated objects that doesn’t move
List the particles in an atom and their respective charges
Proton +1
Electron -1
Neutron 0
What is a charged atom called?
An ion
What materials can be charged by friction?
Insulators
When rubbing a polythene rod and a cloth what item becomes negative (gains electrons) and what item becomes positive (loses electrons) ?
What causes this?
Polythene Rod-Negative
Cloth-Positive
Friction (the triboelectric effect)
Why does a polythene rod gain electrons when rubbed by a cloth bot a perspex rod loses electrons?
As a polythene rod has a higher electron affinity-attracts electrons better, higher up in the triboelectric series.
What type of force occurs between two charged objects?
Non contact force
Fill in the blanks:
Like charges_______
Opposite charges_______
Repel
Attract
What charge creates an electric field going away from itself
Positive
What charge has an electric field going towards itself
Negative
Describe electric field lines:
- They can’t cross they can only bend
- They want to be as short as possible
What does increasing the density of an electric field do?
It increases its strength
What does a Van de Graaff generator do?
It removes electrons from anything touching it to produce a positive charge
What would happen to a person touching a Van de Graaff generator?
Their hairs of the person would stand up on end as the body of the person is all positively charged meaning that the hairs would be repelled
What is the difference between a radial and uniform field?
Radial field-from one point
Uniform field-the lines are straight, neat and ordered usually from one plate to another
From what terminal do electrons flow from and to in a cell?
from negative to positive
What are multiple cells called?
A battery
What does a cell do?
Pushes electrons around a circuit
What does a switch do?
Enables the current in a circuit to be switched on or off
What does an indicator such as a bulb do?
An indicator (such) as a bulb emits light as a signal that current is passing through the circuit
What does a diode do?
Allows current to flow in only one direction
What does a light emitting diode (LED) do?
Allows current to flow in only one direction and emits light when a current is passing through it
What is an ammeter used for?
It is used to measure electric current
What is a voltmeter used for?
It is used to measure potential difference
What does a resistor do?
It limits the current in the circuit-provides resistance
What does a variable resistor do?
It can change the resistance of a circuit
What does a thermistor do?
It decreases resistance as the temperature increases
What does a light dependent resistor (LDR) do?
It decreases resistance as light levels increase
What does a fuse do?
A fuse is designed to melt if the current in a circuit gets too high
How do you draw a wire in a circuit?
You draw it as a straight line or if it needs to change direction at a perpendicular
What materials are wires made from and covered with?
Copper as it is a good, cheap conductor and they are coated in plastic to insulate them
How do you draw /connect a voltmeter in a circuit as opposed to other components
You draw /connect it in parallel to a component as oppose to everything else which is in series-this is to measure the difference in energy before and after a component
What is the formula linking charge flow, current and time?
charge flow = current x time
Q = It
What is the unit of measurement used for charge flow?
couloums
C
What is the unit of measurement used for current?
amperes (amps)
A
What is the formula linking potential difference, energy transferred and charge?
potential difference = energy transferred/charge
V = E/Q
What is the unit of measurement for energy transferred?
joules
J
What is the unit of measurement for potential difference?
volts
V
What is the formula for resistance?
resistance = potential difference/current
R = V/I
What is the unit of measurement for resistance?
Ohms
Ω
What is potential difference?
The measure of energy given to the charge carriers in a circuit
What is current?
The amount of charge carriers in a circuit over a given time
What is resistance?
The opposition in an electrical component to charge
What does increasing the length of a wire do to it’s resistance and why does this happen
The resistance increases due to the electrons colliding in more wire-this increases the temperature of the wire meaning that energy is transferred to a thermal source.
What causes a short circuit?
A short circuit is caused by a shorter route in a circuit (usually by wires touching) and electrons will cause a blockage
Describe the relationship between potential difference and current if the resistance is constant.
There is a positive correlation between potential difference and current as well as them being directly proportional
Describe the relationship between potential difference and current in a circuit with filament lamp
There is still a positive correlation between potential difference and current but current increases proportionately less as oppose to the voltage due to resistance increasing via thermal energy of the filament lamp
Describe the relationship between potential difference and current in a circuit with a diode.
Above 0 there will be a proportionate positive correlation. Below 0 only the voltage will decrease as the current will be blocked and is only allowed to flow one way due to the diode
What is a series circuit?
Where there is only one path for electrons to flow in a circuit
In a series circuit what are the rules for?
1)Current
2)Potential difference
3)Resistance
1)Current-Isn’t split between components
2)Potential difference-Is shared between components
3)Resistance-Equal to sum of resistance for each component :
Total resistance = R₁ + R₂
What is a parallel circuit?
Where there is multiple paths for electrons to flow in a circuit
In a parallel circuit what are the rules for?
1)Current
2)Potential difference
3)Resistance
1)Current-is split between the number of possible paths to the cell
2)Potential difference-isn’t split between components
3)Resistance-If resistors are connected in parallel the supply current is divided between them. The overall resistance is reduced as the current may follow multiple paths.
What is Ohm’s law?
Electric current is proportional to voltage provided temperature remains constant and inversely proportional to resistance
Describe a domestic electricity supply
2 terminals
A direct current
Low potential difference of 1.5-9V
Describe a mains electricity supply
Has an alternating current-frequency of 50Hz (alternates 50x per second and reaches a peak and a trough of 230 and -230 volts)
Has a much higher potential difference of 230V
What are the three wires in a plug and what colours are they?
- Live wire-Brown
- Neutral wire-Blue
- Earth wire-Green Yellow striped
What does the live wire do?
It carries the current
What does the neutral wire do?
It carries the current back to the original power source
What does the earth wire do?
It is connected to the ground-provides an easier route for electricity so that if someone accidentally touches the live or neutral wire they won’t be shocked
Describe the process in which energy is transferred from power stations to our homes and include the voltage
Power station (25KV)->step up transformer->Power lines (132KV)->step down transformer->Factories (33KV) or Homes (230V)
What does a step up transformer do and why is this useful?
Increase voltage, lowers current which lowers resistance and energy lost-good for transporting energy over large distances
What does a step down transformer do and why is this useful?
Decrease voltage, Increases current which is safer for household usage
What causes a short circuit in a plug socket?
The live and the neutral wires touching and this will cause the current to massively increase and cause the fuse inside to blow
What measures are there in place to prevent a short circuit in a plug socket?
All of the wires are insulated so that they don’t touch
What are the pins made of in a plug socket?
Brass as they can’t oxidise in an exposed plug and are hard.
What is the formula for power?
Power = energy transferred/time
P = E/t
What Amperage fuses are domestic households fitted with?
3A, 5A or 13A
What is the formula linking power, current and resistance?
power = current² x resistance
P = I² x Ω
What is the formula for appliance efficiency?
efficiency = output power/input power x 100
