Wednesday, May 30, 2012

CBSE Class X Guess Questions: Science (Magnetic Effect)

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.
2. c) Current induced in a coil due to its rotation in a magnetic field.
3. From the following statement write down that which is applicable to a commutator.                                                    a) galvanometer uses commutator for deadbeat                        b) transformer uses commutator to step up voltage  c) motot uses commutator to reverse the current
4. What is short circuit? When does an electric short circuit occur?
5. How can it be shown that a magnetic field exists around a wire through which current is passing?
6. What will be the frequency of an alternating current if its direction changes after every 0.01 s?
7. 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?
8. 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.
9. Write the principles on which the electric motor and DC generator works.
10. What were the observations made by Oersted in his experiment? State the rule which you use to find the direction of induced current.
11. 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?
12. 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.
13. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
14. Name three colours used and names of the wires used in household wiring.
15. 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?
16. 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.
18. Write the properties of the magnetic field lines. Why don’t two magnetic field lines intersect each other? List three sources of magnetic filed.
19. A positively charged particle (a particle) projected towards north is deflected towards west by a magnetic field. Find the direction of magnetic field.
20. Write the direction of magnetic field at a given point on a current carrying conductor? How can it be represented graphically?
21. At what place of a magnetic field are the magnetic field lines denser? What is direction of magnetic field lines inside a magnet?
22. Explain the function of commutator and the brushes used in an electric motor. Name some devices in which electric motors are used.
23. 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?
Numerical:
1. The mains power supply of a house is through a 5-A fuse. How many 100-W bulbs can be used in
this house at the correct voltage?
2. A wire 10 cm long and carrying a current of 1.5 A is held in a uniform magnetic field in which B=10-
3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.
3. A current of 10 A flows in a circular coil of 1000 turns and radius 0.1 m. Find the magnitude of the
magnetic field at the centre of the coil.
4. At what distance from a straight conductor carrying a current of 2.8 A, will the magnetic induction
be 2.8×10-5 T?
5. Find the strength of the current which will produce a magnetic field of 10-4 T at the centre of a coil
of mean radius 0.10 m. The coil comprises 20 turns.
6. A 0.4 m wire, stretched horizontally, carries an electric current of 15 A from East to West, in a
magnetic field whose magnetic field intensity is 0.1 N/Am, directed vertically downwards. What is (a)
the magnitude of the magnetic deflecting force on the wire, and (b) its direction?