CBSE Important Questions

Section A

Q. 1. What type of image is formed by a plane mirror?

Q. 2. What is the focal length of the plane mirror?

Q. 3. What type of lens does a drop of water behave like?

Q. 4. Name the essential part of human eye.

Q. 5. A concave mirror produces three times enlarged image of an object placed at 10 cm in front of it. Calculate the radius of curvature of the mirror.

Q. 6. Why does the cord of an electric heater not glow while the heating element does?

Q. 7. What is meant by accommodation of eye?

Q. 8. What is the SI unit of power?

Q. 9. How many images are formed by two parallel mirrors?

Q. 10. Check the following statements, write true or false

1. Like magnetic poles attract each other, unlike poles repel.
2. If you strike a sharp edge of metallic knife against the north pole of a bar magnet, it will induce a north pole.
3. The magnetic field produced by a current in a straight wire has no poles.
4. An electric generator is a device that converts electrical energy into mechanical energy.

Q. 11. Where an object should be placed in front of a convex lens to get a real image of the size of the object?

Q. 12. Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s^–1.

Q. 13. Define electrostatic potential at a point.

Q. 14 How are a voltmeter and an ammeter connected in circuit?

Q. 15. Name a device that helps to maintain a potential difference across a conductor.

Section B

Q. 16. Name the type of mirror used in the following situations

1. Headlight of a car
2. Side/rear view mirror of a vehicle
3. Solar furnace

Q. 17. State Snell’s law

Q. 18. State the laws of reflection.

Q. 19. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ώ, 8 Ώ, 12 Ώ, 24 Ώ?

Q. 20. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the find  R/R’.

Q. 21. State Fleming right hand rule.

Section C

Q. 22. State Ohm’s law. What will happen to the current flowing through a conductor if the potential difference is doubled? What is the commercial unit of electric energy?

Q. 23. List the properties of magnetic lines of force.

Q. 24. You are given following current-time graphs from two different sources:

1. Name the type of current in two cases.
2. Identify any one source for each type of these currents.
3. What is the frequency of current in case II in India?
4. Use above graphs to write two differences between the current in two cases.

Q. 25. What are the qualities of an ideal source of energy?

Q. 26. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Q. 27. A child sitting in a class room is not able to read clearly the writing on the black board

1. Name the type of defect from which his eye is suffering
2. With the help of a ray diagram show how this defect can be remedied.

Section D

Q. 28. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification.

 

Q. 29. A household uses the following electric appliances :

1. Refrigerator of rating 400W for ten hours each day.
2. Two electric fans of rating 80W each for twelve hours each day.
3. Six electric tubes of rating 18W each for 6 hours each day.

Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is Rs. 3.00.

Q. 30. Explain the following.

1. Why is the tungsten used almost exclusively for filament of electric lamps?
2. Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
3. Why is the series arrangement not used for domestic circuits?
4. How does the resistance of a wire vary with its area of cross-section?
5. Why are copper and aluminium wires usually employed for electricity transmission.