P2 - Electricity Flashcards
What is electric current?
The rate of flow of electrical charge.
In most circuits, what is the charge that flows to carry the current.
Electrons
What is the word equation for flow of charge?
charge flow = current x time
What is the symbol equation for flow of charge?
Q = I t
At any point in a single closed loop, the current…
is the same.
The current through any component depends on…
the resistance (R) of the component and the potential difference (V) across it.
What is the definition of resistance?
The amount that a component or circuit opposes the flow of current.
What is the unit of resistance?
Ohms, Ω
What is the alternative term for potential difference, that means the same thing?
Voltage
What is voltage?
the pressure from an electrical circuit’s power source that pushes charged electrons (current)
What is the word equation for potential difference?
potential difference = current x resistance
What is a series circuit?
A circuit where all of the components are connected in one loop.
In a series circuit, what can be said about the current, potential difference and resistance?
The current is the same through each component. The total potential difference of the power supply is shared between the components. The total resistance is the sum of the individual resistances.
Why does adding resistors in parallel decrease the total resistance?
There are more routes for electrons to take between the branches, so it is easier for current to flow.
What is DC?
Direct Current (DC) is when current always flows in one direction. It is the current found in circuits powered by a cell or battery.
What is AC?
Alternating Current (AC) is when the direction of current flow rapidly changes, giving an alternating potential difference. It is how mains electricity is supplied in the UK.
What two word equations relate power, potential difference, current and resistance?
power = potential difference x current
power = (current)2 x resistance
What does the amount of energy an appliance transfers depend on?
The power of the appliance and how long it is switched on for.
What does work have to do with electric circuits?
Work is done when charge flows in a circuit.
What is the National Grid?
The National Grid is a system of cables and transformers linking power stations to consumers.
What is a transformer?
A device which alters the potential difference and current of electricity in the cables.
In the branches of a parallel circuit, what can be said about the current, potential difference?
The total current splits between the “branches” of the parallel circuit. The potential difference across each branch is the same.
Describe the current in a series curcuit?
In a series circuit the current is the same as it only has one path to flow through.
How does the Potential Difference vary across two components when connected in series and parrallel?
In series the PD is shared between each component
In parallel the PD across each branch is the same.
If two resistors are connected in parallel what can be said about their total resistance?
Their total resistance is less than the smallest of the two individual resistances.
How should you connect an ammeter in a circuit to measure current?
Ammeters should be connected in series with the component they are measuring the current of.
How should you connect a voltmeter in a circuit to measure PD?
Voltmeters should be connected in parallel to the component they are measuring PD of.
Why is it advantageous to connect lamps in parallel?
If one lamp blows the other ones will still be able to receive current.
What can happen when insulating materials are rubbed together?
They can become electrically charged.
What is the equation for voltage?
V = IR
What is different about current flow through a diode?
Current only flows in one direction because resistance is very high in other direction so prevents current flow.
Why can two insulating materials be electrically charged when rubbed together?
Electrons are transferred.
Material gaining electrons becomes negatively charged.
Material losing electrons becomes positively charged.
What is a non-contact force.
The repulsive or attractive force acting between two charged objects.
What is an electrical field?
A region in which a charged object will experience a non-contact electrical force.
Describe the electrical field around a charged particle.
Strongest closest to the object. Decreases in strength as you move further away.
In situations where sparks are unwanted, what precautions must take place to prevent the build up of static charge?
Any materials that are rubbing together must be earthed to allow the charge to flow off the materials.
State two equations for the power of a circuit.
P = IV, P = I (squared) R
Give the equation for energy transferred. (power)
E = power x time
What two main factors does the energy transferred by an appliance depend on?
Power of the appliance.
How long it is used for.
What three things determine the power of a circuit device?
Amount of energy that was transferred in a given time.
The current running through it.
The voltage across the circuit.
What is the purpose of the National Grid?
To link power stations to consumers so they have access to a source of electricity.
Two types of transformers used in the National Grid.
Step-up transformer
Step-down transformer
What do step-up transformers do?
Increase the voltage so the current can decrease meaning less energy is wasted as heat energy.
What do step-down transformers do?
Increase the current by decreasing the voltage this means that it is safer for domestic use.
Where are step-up transformers found?
Connecting power stations to transmission cables.
Where are step-down transformers found?
Connecting transmission cables to domestic buildings.
Define alternating current.
Current that continuously changes direction, giving an alternating voltage.
Define direct current.
One directional current flow
What are the wires called that connect the electrical appliances to the mains?
Live wire
Neutral wire
Earth wire
What is the purpose of the Earth wire?
In the case of a fault, current will flow to the ground.
What voltage is the neutral wire at?
0 volts
State the voltage between the live and the earth wires.
230 V
What is the purpose of the neutral wire?
To complete the circuit by connecting the appliance back to the mains supply.
For metal appliances where is the earth wire connected to and why?
The metal casing of the appliance.
If live wire becomes loose and touches the metal casing the current will flow through the earth wire, preventing electrocution.
Explain Voltage.
The voltage is the difference from the negative side of the battery, where there is an excess of electrons to the positive side of the battery, where there are less electrons.
It is the pressure from an electrical circuits power source that pushes current.
What is the frequency of the ac manis supply in the UK?
50 Hz
Equation that links energy transferred, charge flow and voltage.
Energy transferred = charge flow x voltage
What is meant by a zero error on the display of an ammeter?
The ammeter displays a reading when not connected to the circuit.
Define diode.
A diode is a device that allows current to flow in one direction but not in the reverse direction.
Define voltage.
It is the pressure from an electrical circuits power source that pushes current.
Where can you find DC?
Found in circuits powered by a cell or battery.
Why do we used AC for the mains supply?
It’s better for transporting current over long-distances.
What equation links energy transferred, charge and voltage?
Energy transferred = charge x voltage
What does Ohms Law state?
The voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions, such as temperature, remain constant.
What is an ohmic conductor?
A conductor that obeys ohms law.
How does resistant change in a filament lamp as voltage increases?
The current increases as the voltage increases, causing the temperature to increase, meaning the resistance increases.
What does energy efficient mean?
A high proportion of the total energy/power input is usefully transferred.
What happens to a LDR resistance as light-intensity decreases?
The resistance increases.
What is a LDR?
Light dependent resistor, are used to detect light levels.
For results to be precise, what do they need to be?
Close together in value.
What is a thermistor?
Temperature sensors, their resistance decreases as temperature increases.
Where are thermistors used?
Fire alarms - when high temperatures are detected, resistance decreases causing a sound to be generated.
What is a diode?
A device that allows current to flow in one direction but not in the reverse direction.
What is a variable resistor?
Moving the position of the slider on this resistor, changes the resistance.
Where are variable resistors used?
some dimmer switches and volume controls.
What is alternating current?
Current that continuously changes direction at a specific frequency.
State the insulation cover used on the earth wire.
Green and yellow stripes
State the insulation cover used on the live wire.
Brown
State the insulation cover used on the neutral wire.
Blue
What happens under normal circumstances in the earth wire.
No current flows through it - however, if a fault occurs, current will flow to the ground.
What potential is the neutral wire at?
0 V
What is the p.d. between the earth and the live wire?
230 V
State an equation linking energy transferred, power and time.
E = P t
State an equation linking energy transferred, charge and voltage.
E = Q V
What is a fuse?
A fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance from overheating.
What is an ohmic conductor?
A conductor where which current and p.d are directly proportional.
Temperature must be constant.
What happens to the resistance of a filament lamp as temperature changes?
Resistance increases.
Metal ions have more energy, causing more collisions with electrons as they flow through metal, causing greater resistance to current flow.
What is a non-contact force in electricity?
The repulsive or attractive force between two electrically charged objects.
What is an electrical field?
The region in which a charged object will experience a non-contact electrical force.
Where are electrical fields found?
Surrounding a charged object.
What is the product of pressure and volume for a fixed mass of gas at a constant temperature?
It is constant.
What happens as resistance increases?
Voltage across the component increases.
What law links p.d. and resistance?
P.d. is shared in proportion to how resistance is shared.
Why is ac supplied in mains?
Because it is easier for travel over long distances with minimum power loss.
Which direction does current flow?
Positive to negative.
Which direction do electrons flow?
Negative to positive.
