Flashcards in P2 Deck (72):
What is an electric current?
A flow of electrons
Where does an electric current flow ?
From negative end to positive end
What do electrons carry?
Energy from the cell. Electrons pass energy to the components in the circuit such as the lamp. In the lamp electrical energy is transferred to thermal and light energy
How much energy are electrons carrying then they get to the positive end?
Less energy than when they started
What is a conventional current?
Arrow used to show the direction of the current. Scientist always draw the current in the opposite direction
What is a series circuit?
Has no branches , current only flows in one path
What is the unit of electricity?
Ampere (A) or amp
How to measure the current in a circuit?
Used an ammeter
What happens to the current when it goes round the circuit?
It is never used up . In a series circuit the current is the same all the way round.
What is a parallel circuit?
What happens to the current in parallel circuits?
Some current goes through different branches . Current in the branches adds up to the total current leaving the cell.
What is the energy transfer in circuits?
-Cells has store of chemical energy
-this is transferred to electrical energy which is carried by electrons passing out the cell
-electrons pass through the components , electrical energy is transferred to other forms of energy
-light energy and thermal in a lamp for examples
What is potential difference?
PD of 1 volt tells us that 1 joule of energy is transferred for each coulomb of charge that is moving through the circuit . It basically shows us where the energy is transferred in an electrical current
Another name for potential difference?
How to measure the potential difference?
What happens to the energy carried by a current ?
Shared between components
What is the rule with potential difference and parallel circuits?
For components connected in parallel the potential difference across each component is the same .
What is a battery?
Two or more cells connected together
What is the potential difference of a battery?
The sum of all the cells potential difference
What direction do cells have to face for battery to work?
The same direction . A cell in the wrong direction will cancel out one of the cells in the right direction.
What is electrical charge measured in?
What is a current of 1 ampere equal to?
1 coulomb of charge flowing per second
What does the size of an electrical current mean?
Rate of flow of electrical charge
How to work out the charge flow?
Q= l x t
Charge flow = current x time
Charge flow , C
Current , A
Time , S
What happens as electrons move through a conductor?
Electrons collide with atoms in the metal. Electrical energy is transferred to other forms , eg thermal
What is resistance?
The potential difference required to drive a current through a component
Equation for resistance?
Resistance = Potential difference / current
Resistance = ohms
Current = A
What is the job of the resistor?
To add resistance to a current if too much energy for one component.
How is the current moving through a resistor and the PD linked?
What cant resistance do?
Change if the current is increased. Resistance is constant
What is a way of describing a resistor?
An ohmic conductor
What can affect how constant a resistor is?
Draw current , PD graph for an ohmic conductor
Draw a current , PD graph for a filament lamp?
Heat effects it , not directly proportional
What happens when a current goes through a filament lamp?
Not directly proportional as the filament lamp gets hot which causes resistance to increase. As the PD increases , the current no longer increases as much
Why does heat effect resistance?
At high temperatures atoms in filament vibrate more. Electrons in the current now collide more with atoms . More energy is needed to push current through the filament .
Describe symbol of LED?
Same as diode just with two arrows of the side.
Features of diodes?
-current flows in one direction
-diode has very high resistance in reverse direction
-very useful in controlling the flow of current in a circuit.
Draw a diodes Pd to current graph?
Stays on the x axis for current in reverse direction. Then lifts up when current is moving forward
What is an LED?
Light emitting diode. They give of light when current flows. They are extremely energy efficient source of light
Rule for resistors on series circuit?
Add together to get total resistance . The current has to pass through each resistor in turn it cant by pass any resistor.
Rule for resistors in parallel?
Total resistance of two resistors in parallel is less that the resistance of the smallest individual resistor
Why resistors in parallel have less resistance than the resistance of the smallest resistor?
With 2 resistors in parallel, we have 2 pathways for the current to take . More total current will flow through the circuit
What happens if the current has increased but the pd has not changed?
Total resistance has decreased
Describe a light dependent resistor symbol?
Symbol of a resistor with a circle around it . Then there are two arrows pointing on to it
What are light dependent resistors?
In the dark , LDR has a high resistance . In the light the LDR has a low resistance
What are thermistors?
The resistance of a thermistor decreases if the temperature increases.
What is power?
Power is the rule at which energy is transferred
What is 1 W in terms of joules?
How to calculate the energy transferred in appliances?
Energy = power x time
What is a direct current?
A current from a cell , flowing in one direction
What electricity does the uk use?
Mains electricity which is an alternating current
What is an alternating current?
Current is constantly changing direction
Why AC electricity supply is good?
Very easy to use a transformer to increase or decrease the potential difference
What is the AC frequency in the uk?
What is the AC potential difference in the uk
What is 1 cycle in mains electricity?
One peak to the next peak
What is the national grid?
A system in how electricity is taken from a power station to our homes. It consists of transformers and high voltage cables
Why is energy always lost in power cables?
The resistance of the wires . You can reduce this energy lose by building power stations next to homes.
How the national grid works ?
1. Electricity passes through the step up transformers with an increase in the PD to several hundred thousand volts
2. Less energy is lost in the power cables when the PD is very high
3. Electricity passes through step down transformers which reduce the pd to 230v.
4. Then it is passed into homes
What connects electricity to mains supply ?
What are the wires made off?
Copper which is a good conductor of electricity . The coating is plastic , which does not conduct electricity
What is the brown wire?
The live wire
What is the live wire?
Carries the alternating potential difference from the supply(230v). The live wire is connected to a fuse in the plug
What is the blue wire?
What is the neutral wire?
Completes the circuit , the pd =0 compared to the live wire
What is the green yellow striped wire ?
What is the earth wire?
This is a safety wire to stop the appliance from becoming live.
Why is the live wire extremely dangerous?
Could be fatal if touched . Even if switch is off, the first part of live wire is still pushing 230v so will still electrocute
What happens if somebody touches the live wire?
A current would flow through a person, into the earth , and they'd be electrocuted
What is the problem with appliances with metal cases?
If live wire becomes loose the case becomes live. Could be fatal if somebody touches the casee