User:Inconspicuum/Physics (A Level)/Electricity Questions

Charge

1. How much charge do 1234 electrons carry?
2. How many electrons does it take to carry 5 C of charge?
3. The total charge on 1 mole of electrons (6 x 10²³ particles) is equal to 1 Faraday of charge. How many coulombs of charge are equal to 1 Faraday?
4. The mass of a ball is 50 mg. It is supplied 5 C of charge. Will there be any change in the mass of the ball? If so, calculate the change of the mass.

Current

1. 10 coulombs flow past a point in a wire in 1 minute. How much current is flowing through the point?
2. How long does it take for a 2A current to carry 5C?
3. In the diagram on the left, I = 9A, and I₁ = 4.5A. What is the current at I₂?
4. What would I equal if I₁ = 10A and I₂ = 15A?
5. In the diagram on the left, in 5 seconds, 5C of charged particles flow past I₁, and 6.7C flow past I₂. How long does it take for 10C to flow past I?

Voltage

1. A battery has an EMF of 5V. What is the total potential difference across all the components in the circuit?
2. The voltages (relative to the voltage of the battery) on either side of a resistor are -6V and -5V. What is the potential difference across the resistor?
3. At a given point in a circuit, 5C of charge have 10 kJ of potential energy. What is the voltage at this point?
4. Why do the electrons move to a point 1cm further along the wire?

Power

1. The potential difference across a 9W light bulb is 240V. How much current is flowing through the light bulb?
2. How much energy is dissipated by a 10W component in 1 hour?
3. The potential difference across a top-notch kettle, which can hold up to 1 litre of water, is 240V, and the current is 12.5 A. 4.2 kJ of energy is required to raise the temperature of 1kg of water by 1°C. Assuming 100% efficiency and that the temperature has to be raised 80°C (20°C to 100°C), how long does it take to boil 1 litre of water?
4. How much energy is dissipated by a 100Ω resistor in 10 seconds if 2A of current are flowing?
5. The charge on an electron is -1.6 x 10^-19 C. How long does it take for a mole (6 x 10²³ particles) of electrons to flow through a 40W light bulb on a 240V ring main?

Resistance and Conductance

1. The potential difference across a resistor is 4V, and the current is 10A. What is the resistance of the resistor?
2. What is the conductance of this resistor?
3. A conductor has a conductance of 2S, and the potential difference across it is 0.5V. How much current is flowing through it?
4. A graph is drawn of potential difference across an Ohmic conductor, and current. For every 3cm across, the graph rises by 2cm. What is the conductance of the conductor?
5. On another graph of potential difference and current, the graph curves so that the gradient increases as current increases. What can you say about the resistor?
6. 3 resistors, wired in series, have resistances of 1kΩ, 5kΩ and 500Ω each. What is the total resistance across all three resistors?
7. 2 conductors, wired in parallel, have conductances of 10S and 5S. What is the total resistance of both branches of the parallel circuit?
8. The circuit above is attached in series to 1 10Ω resistor. What is the total conductance of the circuit now?

Internal Resistance

1. A 9V battery is short-circuited. The potential difference across the battery is found to be 8V, and the current is 5A. What is the internal resistance of the battery?
2. What is the EMF of the battery in the following circuit?

1. What is the internal resistance of the battery in the following circuit?

Potential Dividers

1. A 12 kΩ resistor and a 20 kΩ resistor are connected to a 9V battery. A voltmeter is connected across the 12kΩ resistor. What is the reading on the voltmeter? (Assume negligible internal resistance.)
2. A potential divider consists of 100 5Ω resistors, with a wiper which moves on one resistor for every 3.6° a handle connected to it turns. The wiper is connected to a voltmeter, and the circuit is powered by a 120V power source with negligible internal resistance. What is the reading on the voltmeter when the handle turns 120°?
3. A 9V battery with internal resistance 0.8Ω is connected to 3 resistors with conductances of 3, 2 and 1 Siemens. A voltmeter is connected across the 3 and 2 Siemens resistors. An ammeter is placed in the circuit, between the battery and the first terminal of the voltmeter, and reads 2A. What is the reading on the voltmeter?

Sensors

An LDR's resistance decreases from a maximum resistance of 2kΩ to a minimum resistance of 0Ω as light intensity increases. It is used in a distance sensing system which consists of a 9V power supply, a 1.6 kΩ resistor, the LDR and a multimeter which displays voltage to 2 decimal places measuring the potential difference across one of the two resistors.

1. Across which resistor should the multimeter be connected in order to ensure that, as the distance from the light source to the sensor increases, the potential difference recorded increases?
2. In complete darkness, what voltage is recorded on the multimeter?
3. When a light source moves 0.5m away from the sensor, the voltage on the multimeter increases by 2V. What is the sensitivity of the sensing system when using this light source, in V m^-1?
4. When the same light source is placed 0m from the sensor, the potential difference is 0V. When the light source is 1m away, what voltage is displayed on the multimeter?
5. What is the resolution of the sensing system?
6. Draw a circuit diagram showing a similar sensing system to this, using a Wheatstone bridge and amplifier to improve the sensitivity of the system.
7. What is the maximum potential difference that can reach the amplifier using this new system (ignore the amplification)?
8. If this signal were to be amplified 3 times, would it exceed the maximum voltage of the system? What would the limits on the signal be?

Resistivity and Conductivity

1. A material has a conductivity of 10⁶ S m^-1. What is its resistivity?
2. A pure copper wire has a radius of 0.5mm, a resistance of 1 MΩ, and is 4680 km long. What is the resistivity of copper?
3. Gold has a conductivity of 45 MS m^-1. What is the resistance of a 0.01m across gold connector, 0.05m long?
4. A strand of metal is stretched to twice its original length. What is its new resistance? State your assumptions.
5. Which has the greater resistivity: a plank or a piece of sawdust, made from the same wood?

Semiconductors

1. What is the resistivity of silicon, at room temperature?

1. What sort of variable resistor would a semiconductor be useful in?
2. If positive ions are added to silicon (doping it), how does its conductivity change?