Topic 10 Electricity Flashcards
How do you draw a motor in an electric circuit
Like an ammeter but an M in the middle (MAY NOT BE NECESSARY)
How do you draw a diode in an electric circuit
Like an ammeter, except the circuit wire goes through the circle and instead of an A its a triangle (similar shape to yt logo) and it has a vertical line at the right corner of the circle which isn’t too large but the middle of that line lines up with that corner of the triangle
How do you draw an LED in an electric ciruit
Like a diode but with 2 small arrows pointing (from the circle) outwards
How do you draw a thermistor
Like a variable resistor but you get rid of the arrow and you draw a line parallel to the resistor on the bottom of that diagonal line
How do you draw an LDR
Draw a resistor, then draw a circle around it with 2 small arrows in the top right pointing inside the resistor
Differences between series and parallel circuits
In series circuits, electrical components are connected one after another in a single loop. Voltage is split across components in a series circuit and current remains the same
In parallel circuits, electrical components are connected alongside one another forming extra loops. Voltage is the same across components in parallel but the current splits when there is a junction
Recall that a voltmeter is connected __ _____ with a
component to measure the ________ _________ (______), in
volt, across it
in parallel
potential difference
voltage
Explain that potential difference (voltage) is….
and hence that the volt is…
the energy transferred per unit charge passed
a joule per coloumb
Recall and use the equation:
energy transferred (joule, J) =
charge moved (coulomb, C) × potential difference (volt, V)
E =Q×V
Recall that an ammeter is ______ ___ ________ with a component to measure the _____, in ____ in the component
connected in series
current
amps
Explain that an electric current as
and the current in metals is
the rate of flow of charge
a flow of electrons
Recall and use the equation:
charge (coulomb, C) =
current (ampere, A) × time (second, s)
Q = I * t
If a closed circuit includes a source of potential difference what will happen
In a closed circuit that includes a source of potential difference (voltage) there will be a current flowing around the circuit.
Recall that current is conserved…
at a junction in a circuit
Explain how changing the resistance in a circuit changes the
current and how this can be achieved using a variable resistor
Increasing the resistance in a circuit decreases the current, and decreasing the resistance increases the current.
This is because of Ohm’s Law, which states that current = voltage ÷ resistance (I = V/R).
A variable resistor can be used to change the resistance in a circuit.
By adjusting the variable resistor, you can increase or decrease the resistance, which then controls the current flowing through the circuit.
Recall and use the equation:
potential difference (volt, V)
= current (ampere, A) × resistance (ohm, Ω)
V = IR
Explain why, if two resistors are in series, the net resistance is
increased, whereas with two in parallel the net resistance is
decreased
In series circuits, resistance increases because adding resistors creates more obstacles for current flow, while in parallel circuits, resistance decreases because adding resistors provides more paths for current to flow.
Total resistance in series and parallel circuits
Series:
R(total) = R1 + R2 + R3…
Parallel:
1/R(total) = 1/R1 + 1/R2…
Once you add up all of the resistors with a calculator, flip the fraction around to get R(total)/1
ie: 1/R(total) = 7/20 then R(total)/1 would be 20/7
On a Voltage to current graph, what would a filament bulb, diode and fixed resistor look like
What is the behaviour of the resistance beaches of this
Lets say the current is on the y axis and the voltage is on the x
fixed resistor:
y = x straight graph
Resistance is constant
filament lamp:
y = x graph with hooks on the top and bottom of the graph
Resistance increases as temp increases
diode:
Exponential graph and is at 0 at all times until voltage is around 1 (only allows current to flow in 1 direction)
Resistance is very high in reverse, low in forward (after threshold)
Construct electrical circuits to:
investigate the relationship between potential difference,
current and resistance for a resistor and a filament lamp
Connect a battery, variable resistor, ammeter and whatever you’re measuring (ie: resistor/bulb/diode) in series and a voltmeter around that
Construct electrical circuits to:
b test series and parallel circuits using resistors and filament
lamps
1) Connect a battery, ammeter, switch and 1 resistor in series with a voltmeter around the resistor
2) Record the potential difference, Current and resistance for this resistor
3) repeat steps 1 and 2 but with 2 resistors (make sure the 2nd resistor is the same as the 1st in terms of specs) make sure the voltmeter is around BOTH resistors
4) record potential diff current and resistance for the circuit (series)
5) reorder the resistors to be parallel and the voltmeter is now around the bottom resistor and record potential diff current and resistance for the circuit
Describe how the resistance of a light-dependent resistor
(LDR) varies with light intensity
The resistance of a Light-Dependent Resistor (LDR) decreases as the intensity of light incident on it increases.
In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it.
In bright light, the resistance of an LDR is low, and more current can flow through it.
Describe how the resistance of a thermistor varies with change
of temperature (negative temperature coefficient thermistors
only)
A Negative Temperature Coefficient (NTC) thermistor’s resistance decreases as its temperature increases. This means that as the temperature goes up, the resistance goes down, and vice versa. This relationship is due to the semiconducting nature of the thermistor material.
What is this question asking
Explain how the design and use of circuits can be used to
explore the variation of resistance in the following devices
a filament lamps
b diodes
c thermistors
d LDRs
Explain how you would set up a circuit to do this
ie: ammeter here, battery here, voltage inc by 2 from 2 to 12 etc
Recall that, when there is an electric current in a resistor,
and what can it be described as
there is an energy transfer which heats the resistor. The energy transfer can be described as the result of collisions between electrons and the ions in the lattice
Explain that electrical energy is dissipated as thermal energy
in the surroundings when
an electrical current does work against electrical resistance
Explain ways of reducing unwanted energy transfer
through low resistance wires
power = current2 × resistance
The equation shows that a high current will have a much higher heating effect on the transmission wires than a low current. For this reason, transmitting energy at a high voltage with a low current will keep the wires cooler and waste less energy.
Reducing the resistance of the wires will also reduce unwanted energy transfer, but reducing the current will have a much more significant effect.
Describe the advantages and disadvantages of the heating
effect of an electric current
The heating effect is very useful in appliances which are intended to heat up, such as:
Electric kettles
Electric ovens
Electric toasters
It results in energy loss, reducing efficiency
For example, waste heat in a light bulb or overheating in a computer
It can pose a fire hazard – many domestic fires are caused by too much current passing through low-quality wiring
For example, sparks or excessive heat in an electric motor
Use the equation:
energy transferred (joule, J) =
current (ampere, A) × potential difference (volt, V) × time (second, s)
E = I * V * t
Describe power as…
and recall that it is measured in ____
the energy transferred per second
watt
Recall and use the equation:
power (watt, W) =
energy transferred (joule, J) ÷ time taken (second, s)
P = E/t
Explain how the power transfer in any circuit device is related
to the potential difference across it and the current in it
Potential Difference (Voltage):
Voltage represents the electrical potential energy available to move charge (electrons) through the circuit. It’s the “push” that causes the current to flow.
Current:
Current is the rate of flow of electrical charge (electrons) through a conductor. It’s measured in amperes (A).
Power:
Power is the rate at which energy is transferred or consumed by the device. It’s the product of voltage and current, as stated in the equation P = V * I so they are directly related
Recall and use the equations:
electrical power (watt, W) =
electrical power (watt, W) =
current (ampere, A) × potential difference (volt, V)
P = IV
current squared (ampere2, A2) × resistance (ohm, Ω)
P = I^2 R
Describe how, in different domestic devices, energy is
transferred from batteries and the a.c. mains to the energy of
motors and heating devices
Heating devices such as kettles transfer energy electrically from the mains a.c supply to the thermal energy store of the heating element inside the kettle.
Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor.
Describe direct current (d.c.) as…
and recall that ___ and ______ supply direct current (d.c.)
movement of charge in one direction only
cells and batteries
Describe that in alternating current (a.c.) the movement of
charge _____ ________
changes direction
Recall that in the UK the domestic supply is ____, at a
frequency of __ Hz and a voltage of about ___ V
a.c
50
230
Explain the difference in function between the live and the
neutral mains input wires
The live wire carries the electrical current from the power supply to the appliance, having a potential difference of around + or -230V. The neutral wire completes the circuit by providing a return path for the current back to the power source, typically at 0V.
If the live wire is negative it is relatively negative to the neutral and same for positive
Explain the function of an earth wire and of fuses or circuit
breakers in ensuring safety
The earth wire provides a safe, low-resistance path for current to flow if a fault occurs, preventing electric shocks. Fuses and circuit breakers act as overcurrent protection devices, interrupting the circuit if too much current flows, preventing damage and fire.
Explain why switches and fuses should be connected in the live
wire of a domestic circuit
Safety when switched off:
If a switch were in the neutral wire, the appliance would still be connected to the live wire even when switched off, posing a risk of electric shock if the user touched the appliance.
Fault protection:
If a fault occurs, such as a faulty component touching the metal casing of the appliance, the live wire and the earth wire will provide a low-resistance path for the current to flow. The high current will cause the fuse to melt, breaking the circuit and preventing a shock.
What is the potential difference of the earth wire
0V
This wire is for safety and provides a low-resistance path for current to flow to the ground in case of a fault. It’s usually green and yellow in a UK plug and is at 0 V.
Explain the dangers of providing any connection between the
live wire and earth
Connecting the live wire to the earth wire is extremely dangerous because it creates a low-resistance path for a large current to flow, potentially leading to a severe electric shock or even electrocution.
This occurs because the live wire carries a significant potential difference (+-230V) relative to the earth (0V), and any connection between them will cause a large current to flow.
Describe, with examples, the relationship between the power
ratings for domestic electrical appliances and the changes in
stored energy when they are in use
Explanation:
Power is the rate of energy transfer: Power, measured in Watts (W), indicates how much energy an appliance uses per second.
Higher power, faster transfer:
An appliance with a higher power rating, like a 2000W kettle, transfers more energy per second than a lower-powered appliance, like a 50W lamp.
Energy transfer and use:
Appliances transfer electrical energy to other forms, like heat, light, or motion, to perform their function. The power rating reflects the rate at which this transfer occurs.
A 2000W electric kettle will heat water faster than a 1000W kettle.
A 1500W hair dryer will heat the air faster than a 500W hair dryer.
A 1000W electric fan will produce more airflow than a 500W fan.
