P2 Physics Top 36 Flashcards
What is the definition of current?
Current is the rate of flow of charge
State an equation that links current, charge flow and time. Write down the units of each.
Q = I × t
Q – Charge(coulombs) (C)
I – Current (amps) (A)
T – Time (seconds) (s)
What is the equation that links potential difference, current, and resistance?
V = I × R
What is an IV characteristic?
A graph showing how the current flowing through a component changes is the potential difference across it changes
Explain what happens in a resistor IV graph.
Current increases in proportion to voltage in a directly proportional way
Explain what happens in a filament lamp IV graph
As voltage increases, the bulb gets hotter and resistance increases
Explain what happens in a diode IV graph
A diode only lets current go in One Direction so it has high resistance in the other direction
What happens to the resistance of a filament lamp as the current increases and why?
Temperature increases as current increase increases so resistance increases
What is the effect on current of increasing resistance?
As resistance increases current decreases
What happens to the resistance of a thermistor as it gets hot
As temperature increases resistance increases
What happens to the resistance of an LDR if there is more light?
As light increases resistance decrease
True or false? Potential difference is shared between components in a series circuit.
True
What is the rule for current in a series circuit
Current is the same everywhere
How does the overall resistance of a circuit change when a resistor is added in parallel?
Resistance decreases as more components are added
What is the potential difference and the frequency of UK mains supply
230 V and 50 Hz
Name and give the colours of the three wires in a three core cable
Earth- green and yellow, live- brown, neutral- blue
Describe the useful energy transfer occurs for a battery powered fan
Energy transferred electrically from the battery of a handheld fan to the kinetic energy store of the fans motor
State the equations that can be used to calculate electrical power
Power = current × potential difference (P= I × V)
Power = current² × resistance (P= I² × R)
How are step up Transformers used in the national grid?
Step up Transformers are used to increase the voltage/potential difference
How are stepdown Transformers used in the national grid?
Step down Transformers reduce the voltage/potential difference to safe levels
Describe how you would investigate how the length of wire affects resistance
- Set up the circuit with a power supply, an ammeter to measure current, a voltmeter to measure voltage, and a wire of variable length.
- Connect the wire in series with the ammeter and the power supply.
- Measure resistance for different lengths of the wire using ohms law
- Measure the voltage across the wire using the voltmeter and the current through the wire using the ammeter.
- Record data in a table or graph to show the length of the wire, the measured voltage, the measured current, and the calculated resistance.
- Analyse results and plot a graph of resistance (R) against length (L) of the wire and look at the trend to determine how resistance changes with length.
Describe an experiment to investigate how adding resistors in series and parallel affects the total resistance in a circuit
- Set up the series circuit with a power supply, an ammeter, and multiple resistors in series.
- Measure the total resistance by adding the individual resistances together
- Measure the total voltage across the series circuit with voltmeter and use the ammeter to measure the current.
- Set up the circuit for parallel by connecting the same resistors in parallel and then also measure the total voltage and current again
- Calculate total resistance in parallel and calculate the total resistance using the measured values
- Record data in a table or graph to compare the total resistance in series and parallel
- Analyse how the total resistance changes with the arrangement of resistors.
Explain how an LDR works
As light intensity increases, resistance decreases
Explain how a thermistor works
As temperature increases, resistance decreases
Define potential difference
Energy carried by electrons
Define resistance
Measure of opposition flow to an electrical circuit
What is the order of the national grid beginning with power station?
Power station, step up transformer, pylons, step down transformer, consumers
Where are step up transformers found?
After the power plant, before entering pylons
Where are step down Transformers found
After leaving pylons, before entering consumers
2000 J of energy is transferred over three seconds, what is the power?
P = 2000/3
P = 666.7 W
14,000 W of power is used on a device over a period of two hours. How much energy is transferred?
14,000 = E/120
E =14,000/120
E = 116.6 J
A 900 W microwave is cooking some chicken, 340,000 J of energy is needed to cook the chicken. How much time will it be in the microwave?
P = e/t
900 = 340,000/t
t = 340,000/900
t = 377.8 s
A current of 3 A was passed into a battery over a period of five hours. How much charge was transferred?
Q = 3×300
Q = 900 C
A charge of 18,000 C was transferred passing with a current of 5 A. How long did the current flow for?
18,000 = 5 × T
T = 18,000/5
T = 3600s
A six ohms resistor has a occur passing through of 4 A. What was the potential difference over the resistor?
V = 4×6
V = 20 V
A resistor of two ohms has a potential difference of 4 V. How much current is being passed?
4 = I×2
I = 4/2
I = 2A
