UPSC General Science: Light and Mechanics-1

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Today’s Topic: Light and Mechanics-1

  1. Consider the following statements regarding a motor car battery:

1) Capacity is expressed in ampere-hour.

2) The voltage is usually 12V.

3) Electrodes are lead and copper. Electrodes used is hydrochloric acid (HCI).

Which of the above statements is/are correct?

a) 1 and 2                            b) 2 and 4                   c) 3 and 1                    d) 2 and 3

Ans:     A

Explanation:    In the motor, car battery is of the voltage of 12V usually. A capacity of a car battery is measure/expressed in ampere-hour but statements 3 and 4 is not correct because the electrolyte used in a car battery is sulphuric acid(H2SO4) and electrodes are a lead and red oxide.

2. Why wall of Dam is made thick in bottom because:

a) Liquid pressure increase with depth

b) Liquid pressure decreases with depth

c) Viscosity increases with increase in depth

d) Density of liquid increases.

Ans:     A

3. In thermodynamics, a process is called reversible when:

a) Surrounding and system change into each other.

b) There is no boundary between system and surrounding.

c) The surrounding are always in equilibrium with the system.

d) The system changes into the surroundings spontaneously.

Ans:     C

Explanation:    In thermodynamics, a process is called reversible when the surroundings are always in equilibrium with the system. The reversible process takes a long time to complete. Chemical equilibrium exists in a reversible reaction. IT is a very slow process.

4. What is the Order of Magnitude of electric resistance of the human body (dry)?

a) 102 ohm                   b) 106ohm                   c) 1010ohm                   d) Zero-ohm.

Ans:     B

Explanation:    Human body contains 70-75% of water. It is a good conductor of electricity and heat. Current can be flown through the body it means its resistance is not so large. When the human body (wet) t his time it shows lower resistance than a dry body. Dry body resistance is about 1 megaohm.

5. A ‘black hole’ is a body in the space which doesn’t allow any radiation to come out. This property is due to its:

a) Very low size                     b) Very higher density

c) Very large size                   d) None of these

Ans:     B

Explanation: a Black hole is reason in space in which the gravitational force is so great that no object can escape from it. So, it has a very high density.

6. A spherical body moves with a uniform angular velocity (W) around a circular path of radius (r). Which one of the following is true:

a) It has zero acceleration.

b) It has radial acceleration W2r directed towards the center of the path.

c) Net force along the center is zero.

d) Tangential acceleration is equal to W2.

Ans:     B

Explanation:    When a body moves on a circular path with uniform velocity its tangential acceleration is equal to zero but it has centripetal acceleration.

a Total =

a Total = .

7. Escape velocity from moon surface is less than earth velocity because:

a) atmosphere is not present on moon.

b) Radius of moon is less than earth radius.

c) Moon is more closer to sun.

d) Mass of moon is less.

Ans:     B

Explanation:    Escape velocity – It is the maximum speed, with which body is projected never come back to earth gravitation field.

Ve =

Where g = acceleration due to gravity

R = Radius of the earth/moon

Here, Radius of the moon is less than earth radius so Ve is less.

8. The memory of a computer is commonly expressed in terms of kilobytes or megabytes. A byte is made up of:

a) Two binary digits                       b) Eight binary digits

c) Eight decimal digits                   d) None of these.

Ans:     B

Explanation:    The memory of a computer is measured/expressed in kilobytes or megabytes or gigabytes. One bytes in made of binary digits.

1 byte  = 8 binary digits or

8 binary digits = 1 byte.

9. For reproducing sound, CD (compact disc) audio player uses:

1) Quartz crystal and laser beam

2) Titanium needle and quartz crystal

3) Laser beam

4) Barium titanate ceramic and laser beam

Which of the following statements is/are true?

a) 1 and 4                   b) 2 and 4                   c) Only 3                     d) 1 and 3

Ans:     C

Explanation:    In a compact disc audio player laser beam is used for reproducing the sound.

10. When a compact disc is seen in sunlight, rainbow-like color are seen. This can be explained/based on the basis of phenomena of:

a) Diffraction and transmission                                        b) Reflection and transmission

c) All refraction, transmission and diffraction                   d) None of these

Ans:    C

Explanation:    When we look at the CD we see a rainbow like color. All these three phenomena are the causes for the rainbow-like colors.