Free Physics in Daily Life MCQs with Answers

41. When a ray of sunlight enters a dark room , its straight path become visible because of dust particles hanging in the air. It is because light is _________?

• A. Visible
• B. Transparent
• C. Invisible
• D. opaque
• E. None of these

Explanation: Dust particles scatter visible light into the observer's eyes, making the otherwise invisible path of the beam appear visible. The option 'visible' is the intended choice, although scattering is the actual mechanism.

42. The echo (reflected sounD. will be distinctly heard only at ordinary temperatures if the distance of the reflecting surfaces from the source of sound is at least ________?

• A. 1120 ft
• B. 120 ft
• C. 56 ft
• D. 100 ft
• E. None of these

Explanation: A distinct echo requires the reflected sound to arrive at least 0.1 second after the direct sound. At about 1120 feet per second, the sound travels 112 feet in that time, so the reflector must be half that distance, or 56 feet, away.

43. In winter an iron pipe feel colder than a wooden window . This is because wood is_______?

• A. Conductor
• B. Non-Conductor
• C. Semi- Conductor
• D. Not a solid while iron is a solid
• E. None of these

Explanation: Wood is a poor conductor of heat, so it draws heat from the hand more slowly than iron. Iron therefore feels colder even when both materials are at the same temperature.

44. Water is heated in a kettlE. The inside water is heated by convection. A person sitting near the fire receives heat by ________?

• A. Conduction
• B. Convection
• C. Radiation
• D. Reflection
• E. None of these

Explanation: Heat from a fire reaches a nearby person mainly as infrared radiation, which can travel through space without a medium. Convection heats fluids such as the water in the kettle, while conduction requires direct contact.

45. In a railway track, two rails are joined end to end with a gap tin between them because?

• A. Steel can be saved
• B. Accidents due to contraction in winter can be avoided
• C. Air gaps are necessary for bearing the weight of running train
• D. Accidents due to expansion in summer can be avoided
• E. All of these

Explanation: Steel rails expand when heated in summer. The gaps provide room for this expansion and prevent the rails from bending or buckling.

46. Quartz crystal in quartz watches work on the principle called?

• A. Photoelectric effect
• B. Stark effect
• C. Thermionic effect
• D. Piezo-electric effect
• E. None of these

Explanation: Quartz changes its shape slightly when an electric field is applied and produces an electric signal when mechanically stressed. This piezoelectric vibration provides the very stable frequency used to regulate quartz watches.

47. The term 'Blue Shift' is used to indicate?

• A. Doppler effect in which an object appears bluer when it is moving towards the observer or observer is moving towards the object.
• B. Turning a star from white to blue
• C. In future sun would become blue
• D. Black hole was blue at its start
• E. None of these

Explanation: A blue shift is the movement of spectral lines toward shorter, bluer wavelengths when the source and observer approach each other. It is the opposite of the red shift associated with recession.

48. The half life of a radioactive element is 8-days. How long it take to reduce it from 10 mg to 5 mg?

• A. 4 days
• B. 12 days
• C. 16 days
• D. 8 days
• E. None of these

Explanation: A half-life is the time required for half of a radioactive sample to decay. Since 10 mg becomes 5 mg after one half-life, the required time is 8 days.

49. The number of spark plugs needed in a diesel engine is__________?

• A. 2
• B. 3
• C. 0
• D. 4
• E. None of these

Explanation: A diesel engine ignites fuel through the heat produced by compressing air, so it does not need spark plugs. Spark plugs are used in petrol engines for electrical ignition.

50. Which of the following is most elastic ?

• A. Steel
• B. Rubber
• C. Glass
• D. Sponge
• E. None of these

Explanation: Elasticity means the ability to regain the original shape after deformation, and steel has a higher elastic modulus than rubber, glass or sponge. Rubber stretches more, but greater stretch does not mean greater elasticity in this scientific comparison.