Unit 10 & 11 - Electricity And Circuits/ Static Electricity Flashcards
What are ‘free electrons’?
When the electrons in a metal in the outer shell can easily be removed due to a weak force
What does a voltage do?
It pushes the free electrons around the circuit
What is the direction of a conventional current?
From positive terminal to negative terminal of a battery
What is electric current measured in?
Amperes (amps)
What is current?
The flow of electrons in a circuit (like speed)
What does ‘current being conserved’ mean?
The current leaving the positive terminal is equal to the current arriving at the negative terminal.
What happens to the current in a parallel circuit?
It splits at its branches
What is another name fore voltage?
Potential difference
What 2 things must there be for a current to flow?
The circuit must be closed and there must be a potential difference
How does a bigger p.d affect the current
It is bigger
What is the p.d rule for a parallel circuit?
The total is split evenly across the branches
What is the potential difference measured in?
Volts
How is a voltmeter placed in a circuit?
In parallel around a component
What forms an electric current?
Moving charged particles
What is electric charge measured in?
Coulombs (C)
What is a charge?
The charge that passes the point in a circuit per second
What is electric current?
The rate of flow of charge
What is the equation for charge
Charge = current x time
What is the symbol for current?
I
What is the symbol for charge?
Q
what is electric potential energy?
The energy transferred to the charge from the cell, when something has the ‘potential’ to transfer energy
How is energy transferred in a circuit?
A cell stores chemical energy
Energy is transferred to the charge
That charge transferred energy to components, it has potential energy
Energy transfers to the lamp is transferred to the surrounding by heating and by light.
In terms of energy, what does the potential difference show
The amount of potential energy the cell transfers to each coulomb of charge
What is the equation for energy transfers
Energy transferred - charge moved x p.d
What is the symbol for p.d
V
What is resistance measured in?
Ohms
What is the equation relating p.d, current and resistance
V = I x R
What happens when a resistor is added in a series circuit
The resistance increases
What happens to the resistance when another resistor is added in parallel
The resistance decreases as there are more pathways
What is a variable resistor
A resistor where the resistance can be changed
What does direct proportion mean?
When one factor increases, the other does by the same %
What does it show if the p.d increases but the current doesn’t
The resistance is increasing
What is a diode
A component used in a circuit to keep the current flowing in one direction
What does LDR stand for?
Light-dependent resistor
When does a LDR have a high resistance?
In the dark
What are thermistors
Components that have high resistance at low temperatures
Explain the core practical - Investigating resistance
Set up a simple circuit with resistor around voltmeter and ammeter
Set power pack on lowest voltage and note p.d.
Increase voltage
Repeat with lamps and parallel circuits
Why is energy transferred when a current passes through a resistor and how?
Electrical work is done against the resistance, energy is transferred by heating
What does dissipated mean?
Spread out
Why is it bad for heat to be transferred by heating in a computer
Useful energy is being transferred and wasted
What does the inside of a resistor contain?
Free electrons and a lattice of positive ions
How does a resistor work?
Electrons flow through the lattice and collide with the ions
There is a higher resistance if there are more ions (more collisions) and more energy is transferred
What are the 3 ways resistance can be decreased
Low resistance metals for wires
Thicker wires
Cooling metals (lattice isn’t vibrating as much)
Why might you want to lower the resistance?
So not as much energy is transferred to the surroundings
What is the equation for energy transferred
E = I x V x t
What does the energy transferred by an electric current depend on
The time taken
What is power
The energy transferred per second
What is the equation for power (energy transfer)
P = E/t
What is the equation for power? (Current)
P = I x V
What is power directly proportions to?
The p.d
What is the equation for power (resistance)
P = I^2 x R
What are the mains electricity
A source of energy that appliances use if they need a late amount of energy
What is the national grid
A network of cables and wires that transfer energy by electricity.
What is direct current
When the direction of movement of charge stays the same
What is alternating current
When the direction of the current changes
Why is there alternating current in the mains
It is produced using generators that rotate
What happens to the voltage in alternating current
It increases to a peak, decreases to zero and increases to a peak in the opposite direction
In the UK, how many of the alternating current cycles are there per second?
50
What is the frequency of the mains supply?
50Hz
What is the voltage of the mains in the UK
230V
What are the 4 components in a UK plug?
Earth (green and yellow)
Neutral (blue)
Live (red)
Fuse
What is the role of the earth wire?
Connects metal parts to a large metal tubing in the ground which is at 0V for safety
What is the role of the neutral wire
The return path to the power station, 0V
What is the role of the live wire?
Connects appliances to generators at power station, 230V
What is the role of the fuse?
A safety device that can only carry a certain amount of current, 3A, 5A or 13A
What wire are switches connected to (plug)
Live wire
How does a fuse work
It contains a thin wire, is the current is too high, the wire melts and the circuit is broken
Why are metal parts of appliances connected to the earth wire?
Current from the metal parts of the appliance go into the ground instead of you
Give to examples of the fuse blowing
Too high of a current used
The live wire touches a metal part (a lot of current passes)
What are circuit breakers?
Devices that detect change in the current and can switch off the supply
Give 2 advantages of a circuit breaker
Once a fault is fixed, they can be switched on again and not replaced
They work very quickly (don’t take as long)
Why can plastics collect charge?
They are insulators
What happens to electrons when you rub an acetate rod onto a duster
They move from the acetate to the duster, duster becomes negatively charged and rod positively charged
What is static electricity?
When the charge is not able to flow away to the surroundings, in hair, they begin to repel eachother
What is charging by induction?
When something’s charge changes but no charges have been transferred
Explain how a charged balloon can induce a charge in a wall
The wall contains positive and negative charge. The negative charge is repelled by the negative charge on the balloon so the surface becomes positively charged. The positive charge has been induced
Why might you feel a small electric shock?
If you pick up a charge from a carpet and touch a conductor, the electrons will flow in t(e gap
What does earthed or discharged mean?
When a charge is removed from something
How does static electricity build up in the clouds? (Thunder and lightning)
Friction between particles of ice and water moved by air currents, when the charge is large enough, the particles travel between the cloud and earth
How are buildings earthed?
They have lighting conductors side of thick metal running down from their tops to the earth
Why are sparks dangerous
When there is fuel vapour, it could ignite
What is the danger for refuelling an aircraft
The fuel vapour becomes charged when flying through the air so can ignite
What prevents a spark in an aircraft?
A bonding line is connected to the earth the aircraft before refuelling.
How are cars earthed?
Though their tyres, which contain a form of carbon that makes them conducting
What is electrostatic spraying?
When the nozzle of a spray contains a charge and charges the droplets as they pass, the charged droplets spread out due to repelling and are attracted to the plants by induction
What is a force field?
A volume of space around an object where another object is affected by its force
What metals are of magnetic material?
Steel, iron, nickel and cobalt
What is an electric or electrostatic field?
The force field of a charged object
What is a point charge?
Electric fields around a single point
What are the 4 rules for field lines?
They never cross
Closer together = stronger force
Show direction of charge
Start at positive charge, end at negative charge
What is a rule for an electric field between 2 parallel plates?
It is uniform
