1).Who discovered the magnetic effect of electric current?
i. Fleming
ii. Dalton
iii. Oersted
iv. Faraday
Ans: iii. Oersted
2).Which instrument changes lower a. c. voltage into higher a. c. voltage and vice- versa?
i. Transformer
ii. Dynamo
iii. Inverter
iv. Adaptor
Ans: i. Transformer
3). Which instrument provides electricity in a large scale but causes pollution?
i. Hydroelectric power plant
ii. Thermal power plant
iii. Wind power plant
iv. Solar power plant
Ans: ii. Thermal power plant
4).Who discovered that if there is change in magnetic field linked with a closed coil, an emf is induced in the wire of the coil?
i. Faraday
ii. Maxwell
iii. Oersted
iv. Ampare
Ans: i. Faraday
5).In which of the following, are fossil fuels used?
i. Solar power plant
ii. Thermal power plant
iii. Hydropower plant
iv. Wind power plant
Ans: ii. Thermal power plant
6).For what purpose is the right hand’s grip rule used?
i. To determine magnetic poles of an electromagnet
ii. To determine magnetic field of an electromagnet
iii. To determine magnetic field of a solenoid
iv. To determine magnetic field of a circular wire
Ans: iii. To determine magnetic field of a solenoid
7).Which of the following is used to find the direction of lines of force around a straight wire?
i. Right hand grip rule
ii. Left hand grip rule
iii. Right hand thumb rule
iv. Left hand thumb rule
Ans: iii. Right hand thumb rule
8).Which of the following makes our country rich in hydroelectric power?
i. Presence of high hills and mountains
ii. Presence of a number of rivers
iii. Presence of plain surfaces in Terai
iv. Presence of dense forests in Terai
Ans:ii. Presence of a number of rivers
9). Differentiate between:
a. AC and DC
| AC | DC |
| The flow of electric current regularly changes direction. | The flow of electric current remains in one constant direction. |
| AC is used in homes and businesses for powering most appliances and devices. | DC is often used in batteries, mobile devices, and automotive electrical systems. |
| The voltage in AC constantly changes from positive to negative and back, with no specific polarity. | The voltage in DC remains constant in one direction, with a fixed positive and negative polarity. |
b. Step up and Step down transformers
| Step up transformers | Step down transformers |
| It increases the voltage from a lower level to a higher level. | It decreases the voltage from a higher level to a lower level. |
| The ratio of turns in the secondary coil to the primary coil is greater than 1. | The ratio of turns in the secondary coil to the primary coil is less than 1. |
| Found in devices like microwave ovens, cathode ray tubes, and X-ray machines that require high voltage. | Used in everyday devices like chargers, doorbells, and audio amplifiers to provide suitable voltages for operation. |
C. Electric motor and Generator
| Electric motor | Generator |
| A motor converts electrical energy into mechanical energy, making things move or do work. | A generator converts mechanical energy (from, for example, moving water or steam) into electrical energy. |
| It transforms electrical energy into rotational or linear mechanical energy. | It transforms mechanical energy (often from a turbine or engine) into electrical energy. |
| Used in appliances, vehicles, fans, and machines to create movement or perform tasks. | Used in power plants and other setups to produce electricity for homes, industries, and cities. |
d. Thermal power plant and Wind power plant
| Thermal power plant | Wind power plant |
| Uses heat generated by burning fossil fuels like coal, oil, or gas to produce steam that drives turbines and generates electricity. | Uses the kinetic energy of wind to directly rotate wind turbine blades, which then generate electricity. |
| Produces air and water pollution due to the burning of fossil fuels and other byproducts. It contributes to environmental degradation. | Considered more environmentally friendly as it produces no air or water pollution, and it is a renewable energy source. |
| Can be located anywhere, but proximity to fuel sources (coal mines, oil reserves) is a consideration for efficiency and cost. | Typically located in areas with consistent and strong winds, such as coastal regions or open plains, for optimal electricity generation. |
10).Who founded the law of electromagnetic induction?
Ans:The law of electromagnetic induction was discovered and explained by Michael Faraday.
11).What is motor effect?
Ans: Motor effect is when a magnetic field interacts with an electric current in a wire, causing the wire to move.
12.State the right hand’s thumb rule.
Ans: The right hand’s thumb rule helps to figure out the direction of a magnetic field around a current-carrying wire.
13.State the right hand’s grip rule.
Ans:The right hand’s grip rule helps in understanding the way a wire behaves when placed in a magnetic field.
14.Define magnetic flux.
Ans: Magnetic flux is like the amount of magnetic stuff (imaginary magnetic lines) passing through a surface.
15.What is the working principle of a transformer?
Ans: Magnetic Field Interaction:
Transformers work based on the interaction between a changing magnetic field and a coil of wire. When an electric current flows through one coil, it creates a changing magnetic field.
Induction of Voltage:
This changing magnetic field induces an electric current in another nearby coil, without direct electrical contact. The induced electric current results in a change in voltage, allowing transformers to step up or step down the voltage as needed.
16.Mention the major use of a transformer.
Ans: The major use of a transformer are:
1.Transformers are primarily used to change the voltage of electric current.
2.Transformers help in powering various electrical appliances by providing the appropriate voltage needed for their operation.
3.Industries use transformers to adjust voltage levels for machinery, ensuring they operate efficiently and safely.
17.Which instrument can convert electrical energy into kinetic energy?
Ans:An electric motor is the instrument that can convert electrical energy into kinetic energy.
18.Which instrument can convert kinetic energy into electrical energy?
Ans: A generator is the instrument that can convert kinetic energy into electrical energy.
19.Define electromagnetic induction.
Ans:Electromagnetic induction is like the magic of creating electricity in a wire by waving a magnetic wand nearby. When the magnetic wand moves or changes, it makes the electrons in the wire start to dance, creating an electric current.
20.Write down the type of transformer in which turning of wire in the secondary coil is less than that in the primary coil.
Ans: In Step-up transformer the turning of wire in the secondary coil is less than that in the primary coil.
21.State the principle of mutual induction.
Ans: Mutual induction is when a changing magnetic field in one coil induces a voltage in an adjacent coil.
22.Which type of transformer is used at power stations?
Ans:The type of transformer used at power stations is typically a step-up transformer.
23.State Faraday’s laws of electromagnetic induction.
Ans:Faraday’s laws of electromagnetic induction are like the rules of a dance between electricity and magnetism:
First Law: Magnetic Field Creates Dance Moves:
A changing magnetic field near a wire creates a dance of electric current in the wire.
Second Law: The Bigger, the Better Dance:
The more the magnetic field changes or moves, the bigger the dance of electric current.
24.How is current electricity generated from a bicycle dynamo? Describe in short
Ans: We are going to explain this answer in point:
1.When you pedal your bicycle, it turns a small wheel inside the dynamo.
2.This spinning wheel is connected to a magnet.
3.As the wheel spins, the magnet moves near a wire, creating a changing magnetic field.
4.This changing magnetic field makes the electrons in the wire move, generating electric current.
5.This electric current is then used to power the lights on your bicycle.
25.Clarify Maxwell’s right hand’s grip rule. For what purpose do we use this rule?
Ans:Maxwell’s right-hand grip rule is like a tool to figure out how a magnetic field is circling around a current-carrying wire. Here’s how we use it:
Hold Your Right Hand:
Hold your right hand and extend your thumb, index finger, and middle finger at right angles to each other.
Thumb for Current:
Point your thumb in the direction of the current (the way electrons are moving).
Fingers for Magnetic Field:
Your fingers curled in the direction your fingers naturally curl show how the magnetic field is circling around the wire.
So, this rule helps us visualize and understand the magnetic field pattern created by a current in a wire, which is super helpful in various electrical applications.
26.How can we increase the current produced by a generator?
Ans: To increase the current produced by a generator, we can:
Spin Faster:
Spin the generator (like turning a crank faster) to make the magnetic field move quicker past the wire. Faster movement means more electrons dancing, creating a stronger current.
Add More Wire Turns:
Increase the number of turns in the wire coil inside the generator. More turns mean more electrons dancing, resulting in a larger current.
Boost the Magnetic Field:
Strengthen the generator’s magnetic field. A stronger magnetic field makes the electrons in the wire dance more energetically, producing a larger current.
27.Write the working method of a transformer.
Ans:Here’s how a transformer works in simple terms:
Two Coils and a Magnet:
A transformer has two coils of wire, one called the primary coil and the other called the secondary coil. These coils are wound around a magnetic core, usually made of iron.
Magic of Changing Magnetic Field:
When electricity flows through the primary coil, it creates a changing magnetic field around the coil.
Magnetic Field Talks to the Second Coil:
This changing magnetic field talks to the second coil, the secondary coil, which is close by. The magnetic field encourages electrons in the secondary coil to start dancing and moving.
Dancing Electrons Create Electricity:
The movement of these electrons in the secondary coil generates electric current. This current can be stronger or weaker, depending on the number of turns in the coils.
So, the transformer is like a magical messenger that uses changing magnetic fields to make electrons dance and create electricity in another coil.
28.Describe hydropower plants in Nepal in short. Also analyze their merits and demerits.
Ans:Hydropower plants in Nepal use the energy from flowing or falling water to generate electricity.Nepal, known for its rivers and mountains, has numerous rivers making it ideal for hydropower.Water from rivers is collected in dams or diverted through channels. This water flow spins turbines connected to generators, producing electricity.
Merits of hydropower plants are:
1.Hydropower is a clean, renewable energy source, generating electricity without harmful emissions or pollution.
2.It’s a sustainable source as water is abundant, and hydropower doesn’t deplete natural resources.
3.Operating costs are relatively low once the plant is set up, as water is a free and abundant resource.
4.Provides energy security by reducing reliance on imported energy sources.
Demerits of hydropowerplants are:
1.Can cause habitat disruption, affect aquatic life, and alter ecosystems due to dam construction and water diversion.
2.Construction of dams may lead to the displacement of local communities and loss of their homes and livelihoods.
3.High initial investment and long gestation periods for large hydropower projects.
4.Dependence on seasonal water availability and climate patterns, affecting energy output during dry seasons.
29.Describe thermal power plants in short. Also analyze their merits and demerits.
Ans:Thermal power plants use fossil fuels like coal, oil, or gas to generate electricity.Fossil fuels are burned to produce heat, which is used to convert water into steam.The steam turns turbines connected to generators, producing electricity.Thermal power plants use burning fossil fuels like coal, oil, or gas to make electricity.
Merits of thermal plants are:
1.Thermal power plants provide a reliable and consistent source of electricity.
2.They can generate a large amount of electricity to meet high demand.
3.Suitable for continuous and consistent power supply, serving as base load power plants.
4.Relatively easy to operate and manage once set up.
Demerits of thermal plants are:
1.Release of greenhouse gases and pollutants during fuel combustion, contributing to air pollution and climate change.
2.Consumption of finite fossil fuel resources leading to resource depletion.
3.High water consumption for cooling purposes, posing challenges in water-scarce regions.
4.Generation of solid waste (ash) that needs proper disposal, which can be an environmental concern.
30.Describe a simple experiment to verify Faraday’s law of electromagnetic induction.
Ans:Here’s a simple experiment to verify Faraday’s law of electromagnetic induction:
Materials Needed:
1. A magnet
2. A coil of wire (copper wire is good)
3. A galvanometer or a small light bulb with socket and wires
Procedure:
1.Prepare the Setup:
i. Set the coil of wire on a table or any stable surface.
ii. Attach the galvanometer or light bulb to the ends of the wire coil to measure the electric current.
2.Move the Magnet:
Hold the magnet and move it in and out of the coil of wire. Move it quickly but steadily.
3.Observe the Result:
As you move the magnet, you’ll notice the needle of the galvanometer moving or the light bulb glowing. This shows that moving the magnet near the coil creates an electric current.
4.Reverse the Magnet:
Now, try moving the magnet in the opposite direction or reversing its poles. You’ll still see the galvanometer needle moving or the light bulb glowing.
5.Conclusion:
Faraday’s law is confirmed! Moving a magnet near a coil or changing its magnetic field induces an electric current in the coil. The faster you move the magnet, the stronger the current, confirming the law of electromagnetic induction.
31.How can you obtain magnetic lines of force around a solenoid? Explain in short.
Ans:To see the magnetic lines of force around a solenoid, you can follow these steps:
1. Get a Solenoid:
Obtain a solenoid, which is a coil of wire wrapped around a cylindrical shape.
2. Switch On:
Connect the solenoid to a power source (like a battery) to create an electric current flowing through the wire.
3.Iron Filings:
Sprinkle iron filings around the solenoid. These filings are tiny and will easily stick to the magnetic field.
4. Observe the Pattern:
The iron filings will align themselves along the magnetic lines of force created by the solenoid. You’ll see a pattern forming around the solenoid.
5. Visualize the Field:
The iron filings’ arrangement will give you a visual representation of the magnetic field or magnetic lines of force around the solenoid.
This way, you can observe and understand how the magnetic field is formed around a solenoid using iron filings as indicators of the magnetic lines of force.
32.Write a short note on importance of electric motors in modern life.
Ans:Electric motors power a vast array of everyday items we use, from household appliances like fans, blenders, and washing machines, to industrial machines and vehicles. They make these things work efficiently and smoothly.They make our lives convenient by automating various tasks. Imagine having to wash clothes by hand instead of using a washing machine powered by an electric motor – it saves time and effort.In industries, electric motors power machines that help in mass production and faster manufacturing. This leads to increased productivity and economic growth.Electric motors are essential in medical equipment, wheelchairs, and mobility aids, providing necessary assistance to those with physical challenges, enhancing their quality of life.
33.A hydropower plant is better than a thermal power plant.
Ans:Hydropower is better because it’s clean, doesn’t run out, and costs less to operate than burning fossil fuels used in thermal plants. It’s like nature’s free and green energy source.
34.The core of a transformer is made up of a number of thin iron sheets.
Ans: The core of a transformer is made of thin iron sheets to reduce energy loss and make the transformer work efficiently. These sheets minimize eddy currents, like tiny electric whirlpools, which can waste energy and heat. So, using thin sheets instead of a solid block helps the transformer save energy and perform better.
35. The core of a transformer is laminated with varnish.
Ans:The core of a transformer is laminated with varnish to insulate and protect the iron sheets. This prevents electric currents from flowing across the sheets, which could waste energy and reduce efficiency. The varnish acts like a protective shield, keeping the transformer working smoothly and effectively.
36.Step up transformers are used in power stations.
Ans: Step-up transformers in power stations increase electricity’s power, making it easier to send over long wires with less energy loss. It’s like giving a push to the electricity to travel efficiently.
37.Step down transformers are used in streets.
Ans:Step-down transformers in streets reduce the high voltage from power lines to a lower, usable voltage for homes and businesses, ensuring safety and efficient use of electricity.
38.Electric motor and generator are opposite to each other.
Ans:Electric motors and generators are opposite because one converts electricity into motion (motor), while the other transforms motion into electricity (generator).
39.Electromagnetic induction is a boon for human beings.
Ans:Electromagnetic induction is a boon for human beings because it enables the generation of electricity without direct contact or fuel consumption
40.The numbers of turns in both primary and secondary coils are never made equal.
Ans:The numbers of turns in primary and secondary coils are never made equal to achieve the desired change in voltage.
41.A transformer cannot alter DC.
Ans:A transformer cannot alter DC because it relies on changing magnetic fields, and direct current (DC) has a constant magnetic field. Transformers need this changing magnetic field to induce a current in the secondary coil, which is not possible with a constant magnetic field like in DC.
42.The direction of magnetic lines of force changes when polarity is changed.
Ans:The direction of magnetic lines of force changes when polarity is changed because the magnetic field adjusts its orientation accordingly. Magnetic lines of force are like arrows pointing from the north pole to the south pole of a magnet. When you flip the magnet, these arrows also flip, showing the change in direction of the magnetic field.
43.Electricity and magnetism are interrelated.
Ans:Electricity and magnetism are interrelated because when electric charges move or change, they create a magnetic field. Likewise, a changing magnetic field can induce an electric current.
44.Soft iron core is used in a transformer.
Ans: A soft iron core is used in a transformer because it easily magnetizes and demagnetizes in response to changing currents. It enhances the efficiency of the transformer by intensifying the magnetic field, allowing for effective induction of voltage in the secondary coil.
45. Increasing the number of turns in the coil of a generator increases the current induced by it.
Ans:Increasing the number of turns in the coil of a generator increases the induced current because each turn adds to the overall magnetic interaction, intensifying the generation of electric current.
46. Slip rings are used in an AC generator but split rings are used in a DC generator.
Ans:Slip rings are used in an AC generator because AC changes direction and slip rings allow continuous connection to the external circuit. In a DC generator, split rings are used to ensure the current flows in one direction only, making it suitable for direct current.
47.The lines of force do not intersect each other.
Ans:The lines of force do not intersect each other because if they did, it would mean a magnetic field is pulling in two different directions at the same point, which is not possible.
48. Hydroelectricity is green energy.
Ans: Hydroelectricity is green energy because it is generated using the natural flow of water, a renewable resource. It doesn’t produce harmful pollutants or greenhouse gases, making it eco-friendly and contributing to a cleaner environment
