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CBSE Notes 2011-2012

IMP. For magnatic effect

Magnetic Effect

  1. i. Draw the pattern of the magnetic field lines of current carrying solenoid.

ii. What does the pattern of the field lines inside the solenoid indicate?
iii. Write one application of the current carrying solenoid.

  1. A student performs an experiment to study magnetic effect of current around a current carrying conductor. He reports that –

i. For a given battery, the degree of closeness of a north pole decreases when the compass needle is kept at a point farther away from the conductor.
ii. The direction of deflection of north-pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the same battery sending current in the wire are interchange. Which of the above observations of the student appears to be wrong and why?

  1. a. Explain the meaning of ‘electromagnetic’ and ‘induction’ in electromagnetic induction.

b. On what factors does the value of induced current produced in a circuit depend?
c. Name and state the rule used for determination of direction of induced current.
d. State one practical application of this phenomenon in everyday life.

  1. a. Sketch magnetic field lines around a current carrying straight conductor.

    b. What is meant by the term ‘frequency’ of alternating current? What is its value in India?

c. Why is AC considered to be advantageous over DC for long range transmission of electrical energy?

  1. a. Why does a current carrying conductor kept in a magnetic field experiences force?

b. On what factors does the direction of this force depend?
c. Name and state the rule for the determination of direction of this force.

  1. a. What is magnetic field? How can the direction of magnetic field lines at a place be determined?

b. State the rule for the direction of magnetic field produced around a current carrying conductor.
c. Draw sketch of field lines due to a current carrying straight conductor.
d. What is an electric fuse? What is its function in the circuit?

  1. a. What is solenoid?

b. Draw a sketch of pattern of field lines of magnetic field through and around a current carrying solenoid.
c. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of magnetic field inside and outside the loop.

  1. a. When is the force experienced by a current carrying conductor placed in a magnetic field the largest?

b. State the rule which gives the direction of magnetic field associated with a current carrying conductor.
c. What will be the frequency of an AC, if the direction changes after every 0.02 second?
d. Complete an electric circuit to demonstrate that an electric current carrying wire behaves like a magnet. If a compass needle is placed near the wire, what happens to it on flowing current in the circuit? What happens, if the direction of the current is reversed?

  1. a. What is a uniform magnetic field? Draw a diagram to represent uniform magnetic field.

b. A positively charged particle projected towards east is deflected towards north by magnetic field. What is the direction of magnetic field?
c. State the rule applied by you to find the answer of part (b). d. Describe an activity to show, how you can make an electromagnet in your school library.

  1. Imagine you are sitting in a room with your back to one wall. An electron beam, moving horizontally from front wall towards the back wall, is deflected by a magnetic field to your right side. What is the direction of magnetic field? Name the rule applied. State the rule also.
  2. Draw a labeled diagram of an electric motor. What is the function of a motor? Name three devices in which electric motors are used.
  3. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is

(i). Pushed into the coil,
(ii). Withdrawn from inside the coil,
(iii). Held stationary inside coil.

  1. a. Name any one device which gives

i. Direct current
ii. Alternating current.
b. An alternating current has a frequency of 50Hz. How many times does it change its direction in 1 second?
c. A current through a horizontal power line flows in east to west direction. What is direction of magnetic field
i. at a point directly below it?
ii. at a point directly above it.

  1. a. What is an electromagnet? State two ways, by which the strength of an electromagnet can be increased.

b. On what factors does the magnetic field produced at the centre of a current carrying circular loop depend?
c. State Flemming’s Right hand Rule. How does a solenoid behave like a bar magnet?

  1. An electric motor of 2kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 6A. What result do you expect? Give reasons.
  2. The following diagram shows two straight current carrying wires. Copy the diagram and draw the pattern of lines of force around them and mark their directions.

http://www.cbseguess.com/papers/cbse_important_questions/x/2012/images/4.gif

  1. a. Draw two filed lines around a magnet along its length on its two sides and mark field direction on them by arrow marks.

b. Under what condition is force experienced by current carrying conductor placed in magnetic field max.?
c. On what factors does the direction of force experienced depend when placed in a magnetic field?
d. Describe an activity to show that due to motion of a magnet near the solenoid an induced current is set up in the coil.

  1. a. State the Right Hand rule to find the direction of magnetic field around a current carrying straight conductor.

b. What is electromagnetic induction? Name a device where it is used?
c. Briefly explain different ways to induce current in a coil.

  1. A rectangular coil ABCD is placed between the poles of a horseshoe magnet as shown –

http://www.cbseguess.com/papers/cbse_important_questions/x/2012/images/5.gif
i. What is the direction of force on each arm? ii. What is the effect of the forces on the coil? iii. How is the effect of forces on coil changed
if the terminals of battery are interchanged?

  1. What is overloading of domestic electric circuit? What precautions should be taken to avoid such overloading?
  2. Write the properties of the magnetic field lines. Why don’t two magnetic field lines intersect each other? List three sources of magnetic filed.
  3. A positively charged particle (a particle) projected towards north is deflected towards west by a magnetic field. Find the direction of magnetic field.
  4. Write the direction of magnetic field at a given point on a current carrying conductor? How can it be represented graphically?
  5. At what place of a magnetic field are the magnetic field lines denser? What is direction of magnetic field lines inside a magnet?
  6. Explain the function of commutator and the brushes used in an electric motor. Name some devices in which electric motors are used.
  7. What is an electromagnet? List any of its two uses. Draw a labeled diagram to show how an electromagnet is made. What is the purpose of the soft iron core used in making an electromagnet?
  8. Diagram below shows a circuit containing a coil wound over a long and thin hollow cardboard tube. Copy the diagram

http://www.cbseguess.com/papers/cbse_important_questions/x/2012/images/6.gif
(i). Show the polarity acquired by each face of the solenoid.
(ii). Draw the magnetic field lines inside the coil with directions. (iii). Mention two methods to increase the strength of magnetic field inside the coil.

  1. Draw a labeled diagram of an electric motor. Explain its principle and working. What is the function of split ring in an electric motor?
  2. In the diagram shown alongside-

http://www.cbseguess.com/papers/cbse_important_questions/x/2012/images/7.gif
a. Name the type of current in two cases.
b. Identify any one source for each type of these currents.
c. What is the frequency of current in case (b) in India?
d. Use above graphs to write 2 differences between the current in two cases.

  1. How does a solenoid behave like magnet? Can you determine the North pole and the South pole of a current carrying solenoid with the help of a bar magnet? Explain.
  2. Write the principles on which the electric motor and DC generator works.
  3. What were the observations made by Oersted in his experiment? State the rule which you use to find the direction of induced current.
  4. What constitutes the field of a magnet? How can you show that the magnetic field produced by a given electric current in the wire decreases as the distance from the wire increases?
  5. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
  6. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
  7. Name three colours used and names of the wires used in household wiring.
  8. a. Why does a compass needle get deflected when brought near a current carrying conductor?

b. A rectangular coil of copper wire is rotated in a magnetic field. After what revolutions does the direction of induced current change?

  1. The diagram alongside shows two ways of connecting three bulbs A, B and C to 220 V main in a room. Name the two arrangements. Which of them would you prefer for household electricity? Give two reasons.

  1. State the rule to determine the direction of a

a) Magnetic field produced around a conductor carrying current.
b) The force experienced by current carrying straight conductor placed in a magnetic field perpendicular to it. c) Current induced in a coil due to its rotation in a magnetic field.

  1. What is short circuit? When does an electric short circuit occur?
  2. How can it be shown that a magnetic field exists around a wire through which current is passing?
  3. What will be the frequency of an alternating current if its direction changes after every 0.01 s?
  4. The given figure shows a solenoid wound around an iron core. Will the end A be a North Pole, when the current flows through it in the given direction?