Electricity and Magnetism: Class 10 Science Notes

Electricity and Magnetism Class 10 Science Complete Notes. This note include all the excercise given in electricity and magnetism chapter of science book such as question answer, numericals, give reason, diagrammatic questions and define the following. This note is published for helping students to solve their problems.

If you find any mistakes or feel like giving any suggestions then feel free to comment down.

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  Chapter - 6  
Electricity & Magnetism

2. Answer the following questions:

a.Which wire (live, neutral or earth) connects a switch? Why? 

Ans: Live wire connects a switch so that the socket or appliance is not live when switched off.

b. How can the strength of an electromagnet be increased?

Ans: The strength of an electromagnet can be increased by increasing the current in the coil.

c. What is kWh? How is it related to joule?

Ans: A kilowatt hour (kWh) is the energy produced or consumed when a device with a power of 1 kW produces or consumes energy for one hour.

d. What precautions should we take to avoid electrical hazards in houses?

e. Write Faraday's laws of electromagnetic induction.

Ans: Faraday’s law of electromagnetic induction states, “Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. Likewise, if the conductor circuit is closed, a current is induced, which is called induced current.”

f. How is current electricity generated from a bicycle dynamo? What is motor Effect.

Ans: Dynamo is small electricity generator which works on faradays induction law that tells rotating conductor placed between magnets generates voltage in it. To rotate the copper conductor in dynamo, cycle wheel rotations are coupled mechanically to the dynami rotar which rotates as cycles runs and voltage gets generated in the copper windings of dynamo.

When the current flows through a wire is placed in the magnetic field, a movement is developed in the wire. This phenomenon is called motor effect.

g. State Fleming's right hand rule. For what purpose do we use this rule?

Ans: Fleming’s Right Hand Rule states that if we arrange our thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the current.

Fleming's right hand rule is used to determined the direction of induced current in the conductor when a conductor moves in a region of magnetic field.

h. How do we increase the current produced in a generator?

i. Write the working principle of a transformer.

Ans: A transformer is based on the principle of Faraday's laws of electromagnetic induction and it state that when a conductor is linked with a coil, an emf is induced in it.

j. Mention the major use of a transformer.

Ans: The major uses of transformer are as follows:

• to reduce the voltage of conventional power circuits to operate low-voltage devices
• Transformer is used for Impedance Matching
• The transformer is also used for isolate two circuits electrically
• Transformer is used in the construction of electrical measuring device such as voltmeter, ammeter, relay etc.

k. An electric motor converts energy from one form to another. Name these two forms in sequences.

Ans: An electric motor converts energy from one form to another which is mechanical energy into electrical energy.

l. A dynamo converts energy from one form to another. Name these two forms in sequences.

Ans: A dynamo converts energy from one form to another i.e Mechanical energy into Electrical energy.

m. Describe a simple experiment which illustrates the truth of Faraday's law of electromagnetic induction.

Ans: Experiment:
Two different coils of copper wire having large number of turns (say 50 and 100 turns respectively) are taken. They are now inserted over a non-conducting cylindrical roll, as shown in figure below.

The coil-1, having larger number of turns, is connected in series with a battery and a plug key. Also, the other coil-2 is connected with a galvanometer as shown.

The key is initiated and the galvanometer is observed. We will observe that the needle of th galvanometer instantly jumps to one side and then quickly returns to zero, indicating a momentary current in coil-2.

The coil-1 is now disconnected from the battery. Now we will observe that the needle momentarily moves, but to the opposite side. It means that now the current flows in the opposite direction in coil-2.

Observation 
From these observations, we conclude that a potential difference is induced in the coil-2 whenever the electric current through the coil 1 is changing (starting or stopping). As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it.

This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction.

n.Write down the type of transformer in which turning of wire in the secondary coil is less than that of the primary coil.

Ans: Step down Transformer is the transformer in which turning of wire in the secondary coil is less then that of primary coil.

o. Write a short note on:

i. A.C

Alternating current (A.C.) changes its direction at regular intervals. It is usually defined as the current used in power supplies. It flows in one direction during the first half and in the opposite direction in the next half. The figure (a) in the previous page shows an a.c. circuit. The frequency of electricity supply in Nepal is 50Hz. It means the polarity of the a.c. changes 50 times in one second. The source of the a.c. is an a.c. generator.

ii. Electric bell

An electric bell is a source of sound that converts electrical energy into kinetic energy and then into sound energy.

An electric bell consists of a U-shaped soft iron core around which an insulated wire is wound to make it an electromagnet. A soft iron armature is adjusted in front of the electromagnet. Its one end is fixed while the other end is connected with a hammer which is free to move. Nearby the hammer, a gong is adjusted in such a way that the hammer can beat the gong. The armature is connected with a screw at point x.

iii. Adaptor

An adapter is used to run radio and other electrical appliances which need less voltage to work. It changes the voltage of a.c. supply and it also can change a.c. voltage into d.c. voltage. In it, a knob is used to adjust the required voltage for the electric appliance to run.

iv. Solar battery

Solar battery is an electrical device that changes light energy into electrical energy. It is also called a solar panel. A solar panel is a group of solar cells. It may be mobile or fixed at a place.

The battery or solar panel stores the electrical energy in a storing cell (lead acid battery). The stored electrical energy can be used for different purposes as a source of electricity.

v. Inverter 

An inverter is that electrical appliance which stores electric current when electricity is supplied. During load shedding, it is used as a source of electric current. It is very popular in our daily life. A device connected to an inverter changes the flowing alternating current into direct current an stores in the battery connected to it. When the supply is cut off, the stored direct current in the battery is changed into alternating current by the inverter. The electric current is used for many purposes in our daily life.

vi. Battery charger

Nowadays, battery chargersareused in many electrical appliances. The appliances are also supplied with batteries which stored direct current. They battery chargers change supplied alternating current into direct current to store in the batteries. The direct current stored in the batteries is used to run the electrical instrument. It is also called a recharger. There are many types of chargers. Mobile chargers are very common nowadays. In some battery chargers, there is cut off system as well. The system disconnects the electric circuit when the device is fully charged.

3. Differentiate Between:

a. Step up transformer and step down transformer

Ans: The differences between Step up transformer and step down transformer are as follows: