Electricity and Magnetism
Exact typing reconstruction from the supplied handwritten notes
Original Scanned PDF – View Notes
Lesson – 11
Electricity and magnetism.
2) Difference Between.
(a) AC and DC
| AC | DC |
|---|---|
| The current which magnitude and polarity change at a fixed interval of time is called AC. | The current which flows in perpendicular direction is called DC. |
| It’s full form is Alternating current. | It’s full form is Direct current. |
(b) Dynamo and Generator
| Dynamo | Generator |
|---|---|
| It produces current on small scale. | It produces current on large scale. |
| It is used for low power applications like bicycle. | It is used for a wide range of applications including power plants. |
(c) Motor and Generator
| Motor | Generator |
|---|---|
| It converts electrical energy into mechanical energy. | It converts mechanical energy into electrical energy. |
| It is use in fans, pumps, electric vehicle etc. | It is used in power plants, wind turbines and backup power system. |
(d) Step up transformer and Step down transformer
| Step up transformer | Step down transformer |
|---|---|
| It increases the voltage from the primary side to the secondary side. | It decreases the voltage from the primary side to the secondary side. |
| Converts low input voltage to higher output voltage. | Converts high input voltage to lower output voltage. |
| Used in power plant transmission stations. | Used in local power distribution. |
3) Give reason:
(a) When a ceiling fan is connected to the circuit of the solar panel, the fan doesn’t rotate.
Answer: Because, ceiling fan is rotated by only A.C, But solar panel gives D.C current.
(b) When a magnetic compass is placed near a circuit in which an electric current is flowing, its needle deflects.
Answer: Because of the magnetic effect of electric current.
(c) Electromagnet is used in the electric bell.
Answer: Because, when current is passed through electromagnet it vibrates and makes sound.
(d) The number of primary windings and secondary windings of a transformer are not the same.
Answer: Because if the number of primary winding of a transformers are equal, the AC remains constant and the transformer cannot convert constant AC.
(e) The core of a transformer is laminated.
Answer: The core of a transformer is laminated to avoid leakage of the current outside.
(f) Transformers are used in mobile chargers.
Answer: to convert high AC into low AC which is suitable for charging mobiles.
4) Answer Question:
(a) The frequency of ac in our country is 50 Hz. what does it mean?
Answer: It means that 50 cycle of ac is completed in one second.
(b) Draw the magnetic field lines around the current-carrying straight wire and solenoid.
Current-carrying straight wire
Solenoid
(c) What is the magnetic effect of current?
Answer: The formation of a magnetic field around a conducting wire when electric current is passed through a conducting wire into a circuit is called the magnetic effect of current.
(d) Define magnetic flux.
Answer: The total number of magnetic lines of forces passing through a surface inside the magnetic field is called magnetic flux.
(e) How can the magnetic field produced around straight current carrying be demonstrated by using iron dust, cardboard and conducting straight wire? Explain it.
Answer: Take a square piece of cardboard, pierce it with a straight wire and connect it to an electric circuit and connect the wire to the circuit. place plotting compasses on the cardboard and position them around the wire. Turn on the switch to pass the current in the wire and then observe the needles of compass around on. Because, there is no proper load in the circuit, the switch should be turned off immediately, otherwise, the wire heats up if the
switch is left on for a long time. Swap the poles of the cells and turn the switch on again and observe if the direction of the needles is opposite to the previous one.
(f) What is solenoid?
Answer: A solenoid is a cylindrical wire made of insulated wire.
(g) Write two use of the solenoid.
Answer: They are:
- To make electromagnet.
- To make motor, generator.
(h) What is electromagnetic induction?
Answer: The process of inducing (EMF) or voltage in the conductor when there is a change in magnetic flux in a conductor is called electromagnetic induction.
(i) Study the given picture and write what happens in the following situations:
1) As the bar magnet is slowly introduced into the solenoid.
Answer: There is a small deflation in galvanometer.
2) While introducing the bar magnet rapidly into the solenoid.
Answer: There is large deflation in galvanometer.
3) Holding the bar magnet stationary inside the solenoid.
Answer: There is a constant deflation in galvanometer.
4) On pulling the bar magnet quickly out of the solenoid.
[No answer is written under this point in the supplied source.]
(j) What can be done to increase the magnitude of current produced by a dynamo? write any two ways.
Answer: They are:-
- Increase speed of rotation.
- Increase the magnetic flux.
(k) A simple electric motor constructed by using a coil, paper clips, a drycell and a permanent magnet, is shown in the figure. Explain it’s working process based on motor effect.
Answer: A coil of a motor is formed by winding an insulated wire around a core. Then ac is passed through the coil, when current is passed through the coil and magnetic field develops around it. The coil rotates due to the interaction between the magnetic field of the permanent magnet and that developed the coil. This then rotates the other object attached to it.
The question refers to a figure, but that figure is not present on this supplied PDF page.
(l) What is electromagnetic induction?
Answer: The process where a changing magnetic field generates an electric current in a conductor is called electromagnetic induction.
(m) State Faraday’s law of electromagnetic production.
Answer: It states that induced electromotive force in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.
(n) Draw the magnetic field developed around a straight current carrying wire.
(o) A bulb is connected to a dynamo attached to the tire of a bicycle is not found to be glowing with steady brightness. It was found that the bulb was bright, dimmed and also turned off when the cycle came for rest. mention the reason for such observation based on the working principle of dynamo.
Answer: Because, when the tire of the bicycle is moving fast, the dynamo will produced more electric energy as the tyre slows down the brightness of bulb also falls down and gets completely off when tire stops moving.
(p) Prepare a research report of any two sources of electricity in Nepal including their capacity, type of electricity produced and transmission.
Hydropower in Nepal.
Hydropower: It is Nepal’s main electricity source, contributing over 90% of generation. The country has a potential of 93,000 MW with major project line upper tamakoshi. It’s renewable, reduces fossils fuel reliance and support local development.
Solar Energy in Nepal.
Solar Energy in Nepal: is rapidly growing especially in remote areas without grid access. Nepal enjoy about 300 sunny days in a year, promoting solar installation. It provides clean energy and enhance electricity access.
(q) Write the transformer X and Y shown in the figure.
Answer: The X one is step up transformer and Y one is step down transformer.
(r) Draw the block diagram of the step-up transformer and step-down transformer write two use of each.
Answer: Step down transformer:
It’s two uses are:-
- It is used in mobile charger.
- It helps to reduce high transmission voltage use for safe residential use.
fig: Step down transformer.
Uses of step up transformer:-
- Increase voltage for efficient long-distance transmission.
- Boost voltage from renewable sources to match grid requirement.
5) Solve the following mathematical problems:
(a) To charge a laptop of 20V, a charger with 550 primary turns is connected to an ac source of 220V. Calculate the number of secondary windings of the charger.
Soln,
Vp = 220V.
Vs = 20V.
Np = 550
Ns = ?
We k T,
Vp / Vs = Np / Ns
or, 550 / Ns = 220 / 20
or, Ns = 550 / 11
∴ Ns = 50.
(b) The number of secondary winding of the coil of a transformer used in a microwave oven is 10 times the number of windings in the primary coil. If it is connected to a source of 220V, what is the secondary voltage obtained from the transformer?
Soln,
Np = n
Ns = 10n
Vp = 220.
Vs = ?
We k T,
Vp / Vs = Np / Ns
220 / Vs = n / 10n
Vs = 2200V.
(c) The ratio of the number of the primary winding to the number of secondary windings of a transformer is 22:1. If an adapter with that transformer is connected to an electric circuit having a potential difference of 220V, calculate the output voltage so obtained.
Soln,
Np / Ns = 22 / 1
Vp = 220V.
Vs = ?
We know that
Vp / Vs = Np / Ns
220 / Vs = 22 / 1
Vs = 220 / 22
Vs = 10V.
Discussion
Share a helpful question, idea, or explanation with other students.