UPSC General Science:Sound and Other Mechanics-2

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Today’s Topic :Sound and Other Mechanics-2

1. The half life of radium is 1600 years the fraction of the sample of the radium that would remain after 6400 would be:

a) 1/10                      b) 1/12                      c) 1/16                         d) Zero

Ans:    C

Explanation:    After each 1600 year (64000 year), the substance remaining behind will be 1-[1/2+1/4+1/16] = 1/16. So option (c) is correct.

2. Consider the following statements and select the correct code:

1) In a step-up of transformer, the number of turns in the secondary coil is more than in the primary coil.

2) In the step-down of transformer the number of turns in the primary coil is more than the secondary coil.

a) Only 2 is correct                                       b) Only 1 is correct

c) Neither 1 nor 2 are correct                      d) Both 1 and 2 are correct.

Ans:     D

Explanation:    In a step-down transformer the voltage of secondary coil is also lower than primary coil. In step-up transformer, the voltage of primary coil is lower than in the secondary coil.

3. Which one of the following is/are in correct about infrared spectrum:

1) They have large wavelength.

2) The penetration power of these rays are very high.

3) They show heating effect.

4) They are absorbed by rock salt.

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

Ans:     B

Explanation:    The infrared spectrum are absorbed by glass not by rock salt. The penetration of these are very high on account of which these ray can cross the clouds mist and fag.

4. Which of the following are magnetic substances:

a) Iron                      b) Nickel                      c) Cobalt                      d) All of the above.

Ans:     D

Explanation:    The magnetic substances can be defined those substances which can be attract by ordinary magnets and whose magnetic properties can be easily detected. Iron, Nickel, Steel and Cobalt are magnetic substances so option (d) is correct.

5. The resistance of a uniform wire of length 80cm and of diameter 0.4 mm is found to be 1.34 ohms. The specific resistances of the material would be:

a) 11 x 10-3 ohm                            b) 16 x 10-6 ohm cm

c) 15 x 20-8 ohm cm                      d) 21 X 20-6 ohm cm

Ans:    D

Explanation:    R = S x

(here R = 1.34, 1 = 80 cm, a = π (0.02) 2 cm2)

∴ 1.34 = S x

S = 21 x 20-6 ohm cm.

6. The combined resistance of 8 electric bulb of resistance 200 ohm each connected in parallel would be which one among the following:

a) 0 ohm                      b) 200 ohm                      c) 25 ohm                    d) None of these

Ans:    C

Explanation:    (25 ohm) , (c)

According to question,

8 bulbs connected in parallel

So  8 x  =

R = 25

7. Consider the following statements and select the correct codes:

1) The resistance of alloys generally increases with increases in the temperature.

2) The resistance of pure metallic wire increases when heated and decreases when cooled.

3) There is no effect of temperature on a carbon and insulator.

a) 1 and 3                      b) Only 2 is correct                      c) 1 and 2                    d) 1, 2 and 3

Ans:     C

Explanation:    Carbon, insulator etc. Have their resistance decreases with the rise of temperature, i.e., they have negative coefficient of temperature, so option (c) is correct.

8. Which one for the following correct about shunt:

a) It is a combined resistance of a circuit.

b) It is a resistance connected in series with the galvanometer.

c) It is a fuse wire of a galvanometer.

d) It is a resistance connected in parallel with the galvanometer.

Ans:     D

Explanation:    Shunt is the resistance connected in parallel with the galvanometer conveniently made for safety of galvanometer coils. So option (d) is correct.

9. Which one of the following is used as a fuse in a circuit of larger current:

a) Tinned copper wire                      b) Lead alloy                      c) Silver wire               d) Tungsten wire

Ans:     A

Explanation:    The tinned copper wire is used as a fuse in a circuit of larger current and lead alloy used in a circuit for small current. We also know that the silver is very good conductor of current. Tungsten wire is used in electric bulb filament because it have more and more resistance.

10.Which one of the following is correct sequences of the increasing frequencies of electromagnetic waves:

a) Radio waves, gamma rays, x-rays, infrared, ultraviolet.

b) Radio waves, infrared, ultraviolet, x-rays, gamma rays.

c) Radio waves, ultraviolet, x-rays, infrared, gamma rays.

d) Radio waves, ultraviolet, infrared, gamma rays, x-rays.

Ans:     B


Radio waves               –           104 to 1012 HZ

Infrared                       –           1011 to 4 x 1014 HZ

Ultraviolet                    –           7.6 x 1014 to 1017 HZ

X-rays                          –           1015 to 1020 HZ

Gamma rays                –           109 x 1024