ppe revision physics Flashcards
Define current and state an equation that links current, charge and time, with units for each
current= the flow of electrons moving round a circuit measured in amps (a)
I=Q/t
I=current in Amps
Q=charge in coulombs
t=time in seconds
What is meant by potential difference and resistance in a circuit?
Potential difference (or voltage) is the energy transferred per unit charge between two points in a circuit. It is measured in volts (V) and determines how much energy each coulomb of charge carries.
Resistance is a measure of how much a component opposes the flow of current in a circuit. It is measured in ohms (Ω). A higher resistance means less current flows for a given potential difference.
what is the equation that links current, potential difference and resistance in a circuit?
V=IR,
also known as ohm’s law
explain how you would investigate how the length of a wire changes it’s resistance
Method:
Set Up the Circuit – Connect the wire in a simple series circuit with an ammeter in series and a voltmeter across the wire.
Choose a Starting Length – Attach the crocodile clips to the wire at 10 cm apart, ensuring the wire is straight and measured accurately.
Measure Voltage and Current – Turn on the power supply and record the voltage from the voltmeter and current from the ammeter.
Calculate Resistance – Use Ohm’s Law:
v=IR
to calculate the resistance of the wire.
Repeat for Different Lengths – Move one crocodile clip further along the wire (e.g., 20 cm, 30 cm, etc.) and repeat steps 3–4.
Record and Repeat – Repeat each measurement at least three times for accuracy and calculate an average.
Plot a Graph – Plot a graph of wire length (x-axis) vs. resistance (y-axis) to observe the trend.
Expected Results:
As the length of the wire increases, the resistance increases.
This happens because a longer wire has more atoms, causing more collisions between electrons and atoms, which increases resistance.
The graph should show a directly proportional relationship
what is an ohmic conductor?
a conductor that follows ohms law:
An ohmic conductor is a material that has a constant resistance and follows Ohm’s Law. This means that when you increase the voltage, the current increases at the same rate.
name one linear circuit component and a non-linear circuit component
linear: resistor
non-linear: filament bulb
explain how the resistance of a LDR changes with light intensity.
In Bright Light: The LDR’s resistance is low, allowing more current to flow through the circuit.
In Darkness: The LDR’s resistance is high, reducing the current flow.
what happens to the resistance of a thermistor as it gets hotter?
As the temperature increases, the resistance decreases.
As the temperature decreases, the resistance increases.
true or false?
potential difference is shared between components in a series circuit.
TRUE.
In a series circuit, the potential difference (voltage) is shared between all components.
Each component gets a portion of the total voltage, depending on its resistance. However, the current remains the same throughout the circuit.
how does the current through each component vary in a series circuit?
In a series circuit, the current through each component is the same.
This happens because there is only one path for the current to flow. So, no matter how many components (resistors, light bulbs, etc.) are added to the circuit, the same current flows through all of them.
how does potential difference vary between components connected in parallel?
In parallel circuits, the potential difference is the same across each loop.
explain why adding resistors in parallel lowers the total resistance of the circuit but adding them in series increases the total resistance?
When resistors are added in parallel, the total resistance decreases. This happens because there are multiple paths for the current to flow through, so the overall resistance is reduced. Essentially, adding more resistors in parallel gives the current more routes to take, which allows more current to flow for a given voltage, lowering the total resistance.
When resistors are added in series, the total resistance increases. This is because the current has to pass through each resistor one by one, encountering more opposition to flow at each resistor. The total resistance is simply the sum of the individual resistances.
true or false? Mains electricity supply is an alternating current.
TRUE.
what is the potential difference and frequency of the UK mains supply?
potential difference= 230 V
frequency= 50 hz
name the colours of wire and what they mean in a 3 pin plug
Live - Brown
Neutral - Blue
Earth - Yellow and Green
what is the power rating of an appliance?
The power rating of an appliance is the amount of energy it uses per unit of time, typically measured in watts (W) or kilowatts (kW). It tells you how much electrical power the appliance consumes when it is operating at its normal usage.
explain why electricity is transported but the national grid at low current but high potential difference.
reduces energy loss as heat
what is the function of step up and step down transformers?
step up transformers increase the potential difference and Lower the current
step down transformers increase the current and lower the potential difference
