Leaving Cert Homework

Static Electricity.
Section 1.
Q1. What is static electrcity?
Q2. Give some everyday examples of where static can occur.
Q3. What physical unit is static measured in?
Q4. Why does static build up on particular objects and not on others?
Q5. Why do tall buildings have a lightening conductor?

Section 2.
Q1. State Coulomb's law.
Q2. Coulomb's law is referred to as an inverse square law. What does this mean?
Q3. Two 5 Coulomb charges are placed side by side. Do they feel a force of attraction or repulsion?
Q4. What is meant by the permitivity of a substance?
Q5. If a block of glass has a relative permitivity of 81, what is the permitivity of the glass?

Section3.
Q1. A 3 coulomb and a 5 coulomb charge are placed 4m appart in a vacuum. What is the force acting on these charges? Is the force attractive or repulsive?
Q2. A -3 coulomb charge and an 8 coulomb charge are placed 5m appart in a vacuum. waht is the force on these charges and is it attractive or repulsive?
Q3.State Coulomb’s law of force between electric charges.
Q4.Why is Coulomb’s law an example of an inverse square law?
Q5. Give two differences between the gravitational force and the electrostatic force between two electrons.

Section4.

Q1.Show how to charge an object by induction. Include diagrams
Q2.Draw a labelled diagram of a gold leaf electroscope and list any three uses of it.
Q3.State Coulomb’s Law in words.
Q4.Two point charges of +2microCoulombs and –3microCoulombs are 50 cm apart in air. Find the magnitude and direction of the force on the 2 µCoulomb charge.
Q5. The relative permittivity of water is 81. Calculate the actual permittivity of water.

Section 5.

Q1. If the elctric field strength is 6NC-1 and the charge experiences a force of 3N. what size is the charge?
Q2. Find the electric field strength at a distance of 10mm from an electron in a dieletric of relative permitivity equal to 6.
Q3. The dome of a Van de Graff generator is charged. The dome has a diameter of 30 cm and its charge is 4 C. A 5 μC point charge is placed 7 cm from the surface of the dome.
Calculate:
(i) the electric field strength at a point 7 cm from the dome
(ii) the electrostatic force exerted on the 5 μC point charge.

Section 6.
Q1. This is a past exam paper question and was therefore worth 14% in the exam.

(a) Why is a lightning conductor made of copper?

(b) What is meant by electric field strength?

(c) Why do the ions near the lightning conductor accelerate?

(d) How does the presence of ions in the air cause the air to be more conducting?

(e) How do the charged clouds become neutralised?

(f) What are the two ways in which a lightning conductor prevents a building from being damaged by lightning?

(g) Why are raised umbrellas and golf clubs not recommended during thunderstorms? Act as (lightning)

(h) Explain why pointed surfaces should be avoided when using high voltage electrical equipment.

Potential difference and Capacitance Current & Charge.

Section 1.

Q1.Define (i) potential difference, (ii) capacitance.

Q2. The potential difference between two points is 12 Volts. Find the work done in transferring a charge of 8 C between the points.

Q3. The potential difference between two points is 2000 Volts. An electron (of charge 1.6 x 10-19 C and mass 9 x 10-31 kg) is released at one of the points and moves towards the other under the action of the field. Find its speed when it arrives at the second point.

Q4.Describe briefly (with the aid of diagrams) how you would demonstrate that a capacitor can store energy.

Q5.A capacitor of capacitance 2 uF is charged to a potential difference of 200 Volts. Find the energy stored in it.

Section 2.

Q1. Leaving Cert Higher 2011. You will have to look up the experiment part of this question.

(i)     How does a full-body metal-foil suit protect an operator when working on high voltage power lines?

(ii)   Describe an experiment to investigate the principle by which the operator is protected.

Section 3.

Q1. What is the force on a charge of -8 micro-coulombs in an electric field strength of 6.4 × 103 N C–1.

Q2. A conductor has a potential of 60.5 V when a charge of 14 micro-coulombs is placed on it. What is its capacitance?

Q3. Find the magnitude of the electric field strength at a distance of 7.2 m from a charge of 3.5 micro-coulombs.

Q4. The potential difference between two points is 3300 V. A proton is released at one of the points and moves towards the other end under the action of the field. Find its speed when it reaches the second point.

Q5. A capacitor of capacitance 8 micro-farads is charged to a potential difference of 400 V. Find the energy stored.

Section 4.

Q1. What ishe capacitance of a capaitor with energy of 5x10-2j stored at a voltage of 12V?

Q2. What are the factors that effect the capacitance of a parallel plate capacitor?

Q3. Describe an experiment to show that a capacitor can store energy.

Q4. A capacitor in air has plates of area 50cm2 overlapping 1mm apart. find its capacitance.

Q5. Find the area of overlap of the plates of a capacitor with capacitance 2x10-4f ,0.5 mm apart in air.

Section 5.

Q1. Find the amount of charge that has passed in a circuit that has a charge of 3 amps flowing for 12 seconds.

Q2. Find the amount of charge that passes a point in a circuit which has a current of 1 amp flowing for one second.

Q3. How much work is done in a circuit carrying 4amps for one minute if the resistance of the circuit is 50 Ohms.

Q4. How many electrons pass a point in a circuit in 10 seconds if a current of 3.5 amps is flowing?

Q5. Explain the term amps.

Section 6.

Q1. What power is flowing in a circuit with voltage of 10 and a current of 6 amps?

Q2. How much charge passes a point in a circuit in which a steady current of 8 A flows for 2 hours?

Q3. Draw a diagram in which you could show the three effects of an electric current.

Q4. A device drawing 4 amps is connected to the mains electrcity. what is the power consumption of the device?

Q5. With regard to current flow explain the major differences between a capacitor and a diode.

Section7.

Q1. What is the voltage in a circuit when 4 12v batteries are connected in series?

Q2. What is the motivation behind transmitting power at high voltages?

Q3. What is the total voltage when five 12 volt batteries are connected in parallel?

Q4. Give the three effects of an electric current and draw a diagram of the set up of the apparatus you could use to show all three.

Q5. What is the charge carrier in a metal conductor?

Section 8.

Section 9.

Section 10.

Q1. Why is high voltage used for the transmission of power?

Q2. Sketch the graph you would expect to see if you were comparing voltage to current in a bulb, a semiconductor, a gas and a vacuum.

Q3. For the graph sketches in Q2 above explain why the graph looks like it does.

Q4. describe how you would wire a standard plug.

Q5. Give another term for bonding.

Semiconductors

Section 1.

Q1. What is the difference between intrinsic and extrinsic semicondution?

Q2. When doping a silicon semiconductor to p-type what element is used? What element is used for doping to n-type?

Q3. Describe why the current in a semiconductor diode can increase as its temperature increases.

Q4. How is a p-n junction constructed?

Q5. Semiconductors are considered to be a possible replacement for copper in wiring. Give an advantage and a disadvantage of using semiconductor material in wiring.

Section 2.

Q1. Draw a diagram of a semiconductor diode doped n-type.

Q2. What is meant by extrinsic conduction?

Q3. Explain how a p-n junction is formed.

Q4. Sketch the diagram you would expect to see when comparing current to voltage fro a semiconductor diode like a thermistor. Explain why your graph has the shape it does.

Q5. Draw a diagram of a circuit with a semiconductor diode in forward biased. Explain what happens to the diode in order to allow current to flow when the circuit is in this configuration. What is going on at the p-n junction when a diode is placed in reversed biased in a circuit?