MAGNETIC EFFECTS OF ELECTRIC CURRENT– 2020 Important Questions

1 MARK QUESTIONS [ VERY SHORT ANSWER]

Q1. What is meant by a magnetic field?

Q2. How is the direction of magnetic field at a point determined?

Q3. Why are magnetic field lines closed curves?

Q4. Mention the shape of the magnetic field lines around a current-carrying straight conductor.

Q5. What type of core used to make an electromagnet?

Q6. Name the rule which gives the direction of induced current in a conductor.

Q7. State the rule which is used to find the direction of induced current.

Q8. How can it be shown that a magnetic field exists around a wire through which a direct current is passing?

Q9.  In a domestic electric circuit, mention the potential difference between live wire and neutral wire and frequency of AC?

Q10. What is the advantage of the earth wire connection in domestic electrical circuits?

Q11. Which is the most important safety method used for protecting home appliances from short-circuiting or overloading?

Q12. List two sources of magnetic fields.

Q13. Define the term ‘induced current’.

Q14. When a current-carrying conductor is kept in a magnetic field, state the position when maximum force acts on it.

Q15. State the conclusions that can be drawn from the observation that a current-carrying wire deflects a magnetic needle placed near it.

Q16. Mention the angle between a current-carrying conductor and magnetic field for which the force experienced by this current-carrying conductor placed in magnetic field is largest.

Q17. Suggest one way of discriminating a wire carrying current from a wire carrying no current.

Q18. Name any two sources of direct current.

Q19. Mention the advantage of A.C. over D.C. for long-distance transmission.

Q20. List anyone point of difference between A.C. and DC.

Q21. What is Short Circuit?

Q22.  Mention the name of three colours of the wires used in household wiring.

Q23. In which wire in an AC housing circuit, is the switch introduced to operate the light?

Q24. Why is an alternating current considered to be advantageous over direct current for long-range transmission of electric energy?

Direction (Q No. 25-29)In each of the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(b) If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

(c) If Assertion is true but Reason is false.

(d) If Assertion is false, but Reason is true.

(e) If Assertion and Reason both are false.

Q25. Assertion: A current-carrying conductor experiences a force in a magnetic field.

Reason: The force acting on a current-carrying conductor in a magnetic field is due to interaction between magnetic field produced by the current-carrying conductor and external magnetic field in which the conductor is placed.

Q26. Assertion: Electric Motor converts Electric Energy into mechanical Energy.

Reason: Electric motor is based on the principle of Flemings right-hand rule.

Q27. Assertion: Magnetic field lines do not intersect each other.

Reason: There cannot to two direction of the magnetic field at a point.

Q28. Assertion: The principle of Electromagnetic Induction was discovered by Michael Faraday.

Reason: The principle is used only in DC generators.

Q29. Assertion: Magnetic field can be created using a solenoid.

Reason: The strength of the magnetic field will depend on the number of turns of the solenoid.

Q30. The most important safety method used for protecting home appliances from short-circuiting or overloading is

(a) earthing

(b) use of fuse

(c) use of stabilizers

(d) use of electric meter

Q31. The essential difference between AC generator and DC generator is that

(a) AC generator has electromagnet while DC generator has permanent magnet

(b) DC generator generates higher voltage

(c) AC generator generates higher voltage

(d) AC generator has slip rings while DC generator has commutator

Q32.  The phenomenon of electromagnetic induction is

(a) the process of charging a body

(b) the process of generating magnetic field due to current passing through coil

(c) the process of producing induced current in a coil due to relative motion between a magnet and the coil

(d) the process of rotating a coil of an electric motor

Q33.  Which of the following property of a proton can change while it moves freely in a magnetic field?

(a) Mass

(b) Speed

(c) Velocity

(d) Momentum

Q1.  How does the strength of magnetic field due to a current-carrying conductor depend upon

(i)  distance from-the conductor?

(ii)   current flowing through the conductor?

Q2. Under what conditions permanent electromagnet is obtained, if a current-carrying solenoid is used?  Support your answer with the help of a labelled circuit diagram.

Q4.  What is an electric fuse?  What is its role in electric circuits? Should it be placed on neutral wire or on live wire?  Justify your answer.

Q5. What does the magnetic field pattern inside the solenoid indicate? State how this field be utilised to make an electromagnet. List two ways by which strength of this magnet can be increased.

Q6. Explain briefly two different ways to induce current in a coil. State the rule which determines the direction of induced current.

Q7. Explain whether an alpha particle will experience any force in a magnetic field if:

(i) It is placed in the field at rest.

(ii) It moves in the magnetic field parallel to field lines.

(iii) It moves in the magnetic field perpendicular to field lines.

Q8. How would the strength of magnetic field due to current carrying loop be affected if:

(i) Radius of the loop is reduced to half its original value?

(ii) Strength of current through the loop is doubled?

Q9. What is short-circuiting?   State one factor/condition that can lead to it. Name a device in the household that acts as a safety measure for it. State the principle of its working.

Q10. (a) Give the significance of the following in a domestic circuit:

(i) Electric meter

(ii) Earthing

Q11. List three factors which can cause overloading of domestic electric circuits.

Q12. The flow of current in a circular wire creates a magnetic field at its centre. How can existence of this field be detected? State the rule which helps to predict the direction of magnetic field.

Q13.  (i) What do you understand by the term short circuit? How does it occur?

(ii) What are the consequences of short circuit?

(iii) Give two examples for application of heating effect of electric current.

Q14.      A magnet AB is broken into two pieces. Point out the polarity of A, B, C and D.

Q15.  A small valued resistance XY is connected across the ends of a coil. Predict the direction of induced current in the resistance XY when

(i)  South pole of a magnet moves towards end A of the coil.

(ii)  South pole of a magnet moves away from end A of the coil.

5 MARKS QUESTION [ LONG ANSWER]

Q1.  Explain with the help of a    labelled diagram, the distribution of magnetic field due to a  current through a  circular loop. Why is it that, if a current-carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn?

Q2.         (i)  Draw the magnetic field lines through and around a single loop of wire carrying electric current.

(ii)   State whether an α-particle will experience any force in a magnetic field, if (α-particles are positively charged particles).

(a)  It is placed in the field at rest.

(b)  It moves in the magnetic field parallel to field lines.

(c) It moves in the magnetic field perpendicular to field lines. Justify your answer in each case.

Q3. Explain, why electric power transmitted at high voltages and low currents to distant places?

Q4. (i) What is a solenoid?

(ii) Draw the pattern of magnetic field formed around a current-carrying solenoid. Compare this field to that of a bar magnet.

(iii) Explain an activity to show that a current-carrying conductor experiences a force when placed in a magnetic field.

Q5. (i)  A coil of insulated copper wire is connected to a galvanometer. What happens if a bar magnet is:

(a) Pushed into the coil?

(b) Withdrawn from inside the coil?

(c) Held stationary inside the coil?

(ii) Mention one more method of inducing current in a coil.

Q6. (i)  A stationary charge is placed in a magnetic field.  Will it experience a force? Give reason to justify your answer.

(ii) On what factors does the direction of force experienced by a conductor when placed in a magnetic field depend?

(iii) Under what conditions is the force experienced by a current-carrying conductor placed in a uniform magnetic field maximum?

(iv) Name and state the rule which gives the direction of force experienced by a current carrying conductor placed in a magnetic field.

Q7. (a) Define electromagnetic induction.

(b) Two coils P and S are wound over the same iron core. Coil P is connected to battery and key and the coil S is connected to galvanometer. Write your observations when:

(i)  Current in the coil P is started by closing the key.

(ii) Current continues to flow in coil P.

(iii)Current in coil P is stopped by removing the key.

Explain the reason for such observation.

Q8. (a) Draw a schematic labelled diagram of domestic electric circuit.

(b) Why is it necessary to provide-

(i) A fuse in an electric circuit

(ii) An earth wire to electric application metallic body? Explain.

Q9. (i) Explain what is the difference between a direct current and an alternating current. Write one important advantage of using alternating current.

(ii) An air conditioner of 2kW is used in an electric circuit having a fuse of 10A rating. If the potential difference of the supply is 220 V, will the fuse be able to withstand, when the air conditioner is switched on? Justify your answer.

Q10. (i) Explain two safety measures commonly used in electric circuits and appliances.

(ii) An electron enters a magnetic field at right angles to it as shown in figure. What will be the direction of force acting on the electron? State the rule which gives direction of force on electron.

(iii) If instead of electron, a neutron enters a field, what will be its direction of motion? Give reason for your answer.

Q11.  (i) How does the strength of magnetic field due to current carrying conductor depends upon the current flowing and distance from the conductor?

(ii) α-particles are positively charged particles.  State whether an a-particle will experience any force in a magnetic field, if

(a) it is placed in field at rest.

(b) it moves in the magnetic field parallel to field lines.

(c) it moves in the magnetic field perpendicular to the field lines. Justify your answer in each case.

Q12. Explain with the help of a labelled diagram, the distribution of magnetic field due to current-carrying coil that has n turns, such that the field produced at any point is n times as large as that produced by a single turn.

Q13.  You are given the following current-time graphs from two different sources: