31. An electron of mass 9.1 x 10−^{31}kg moves with a speed of 2.0 x 10^{6}ms^{−1} round the nucleus of an atom in a Circular path of radius 6.1 x 10^{11} Calculate the centripetal force acting on the electron.

**A.**7.7 x 10^{47}N**B.**6.0 x 10−8N**C.**3.0 x 10^{−14}N**D.**1.3 x 10^{−26}N

**Correct Option: Answer is C**

Centripetal force (Fr) = MV2/r

**32. **A device consumes 100 W of power when connected to a 120 V source. Calculate its resistance.

**A.**1.2Ω**B.**12,000 Ω**C.**20.0Ω**D.**144Ω

**Correct Option: Answer is A**

R = v/I

= 120/100= 1.2Ω

**33. **Which property of a wave remains constant when the wave travels from one medium into another?

**A.**Amplitude**B.**Wavelength**C.**Velocity**D.**Frequency

**Correct Option: Answer is A**

**34. **The anomalous expansion of water occurs in the range

**A.**0 °C to 100 °C**B.**0 °C to 4 °C**C.**4 °C to 100 C**D.**-4 °C to 0 °C

**Correct Option: Answer is B**

**35. **A ray of light travelling from a rectangular glass block of refractive index 1.5 into air strikes the block at an angle of incidence of 30. Calculate its angle of refraction.

**A.**48.6°**B.**19.5°**C.**20.0**D.**45.0

**Correct Option: Answer is A**

n = sinI/sinr=sin30^{o}/sinr

1.5 = sin30^{o}/sinr

1.5 sin r = sin30^{o}/1.5 = 0.5/1.5

sin r = 0.3333

= 48.6^{o}

**36. **A rectangular piece of iron measuring 4 cm by 3 cm at 20^{o}C is heated until its temperature increases by 100 C. Calculate the new area of the metal. [Linear expansivity of iron is 1.2x 10^{−5}K^{−1}]

**A.**12.0144 cm^{3}**B.**12.0346 cm^{3}**C.**12.0288 cm^{3}**D.**12.0173 cm^{3}

**Correct Option: Answer is B**

Linear expansivity (α)

= A_{2}−A_{1}/A_{1}θ

Original Area(A_{1}) = 4 x 3 = 12

New Are (A_{2}) = ?

Temp. rise (θ) = 100^{o}C

A_{2} – 12 = 1200 x 1.2 x 10^{−5}

A_{2 }– 12 = 1440 x 10^{o}C

A_{2} – 12 = 0.0144

A_{2 }= 12.0144 cm^{2}

**37. **Which of the following graphs gives the correct relationship between energy and mass when mass is converted to energy?

**A.**A**B.**B**C.**C**D.**D

**Correct Option: Answer is A**

**38. **The diagram above illustrates an object moving in a circular path at a constant speed. Which of the arrows indicates the direction of linear velocity?

**A.**z**B.**X**C.**Y**D.**W

**Correct Option: Answer is A**

**39. **Which of the following thermometers is used to measure the temperature of the human body?

**A.**Thermocouple**B.**Alcohol-in-glass thermometer**C.**Gas thermometer**D.**Platinum resistance thermometer

**Correct Option: Answer is A**

**40. **In the diagram above, the time taken to trace a wave between P and Q is

**A.**2 periods**B.**1 period**C.**1 1/2 periods**D.**1 1/4 periods

**Correct Option: Answer is B**

**41. **Which of the following materials does not serve as a safety device in electrical circuits?

**A.**Connecting wires**B.**Earth wire**C.**Fuse**D.**Switch

**Correct Option: Answer is A**

**42. **Which of the following liquids has the highest surface tension?

**A.**Soapy water**B.**Cold water**C.**Hot water**D.**oily water

**Correct Option: Answer is D**

**43. **The nucleon and proton numbers of a neutral atom of an element are 238 and 92 respectively. Determine the number of neutrons in the atom.

**A.**119**B.**330**C.**165**D.**146

**Correct Option: Answer is D**

Neutron No (N) = 238 – 92

= 146

**44. **An instrument used to measure relative humidity is the

**A.**hygrometer**B.**hydrometer**C.**pyrometer**D.**manometer

**Correct Option: Answer is A**

Hygrometer, instrument used in meteorological science to measure the humidity, or amount of water vapour in the air. Several major types of hygrometers are used to measure humidity.

**45. **The area under a velocity-time graph represents

**A.**speed**B.**acceleration**C.**moment**D.**distance

**Correct Option: Answer is D**

The area under the velocity-time graph represents the distance travelled. Velocity-time graph for a car moving with uniform acceleration is a straight line and the area of the graph gives the distance travelled during a time interval.