Physics: Light, Sound, Electricity and Mechanics MCQs

Solved general science MCQs on mirrors and lenses, eye defects, sound and ultrasound, household electricity, motors and transformers, energy and buoyancy.

1. 1

   The sky appears blue because of the:

   Arefraction of light by cloudsBreflection of light by oceansCabsorption of red light by dustDscattering of light by air molecules

   Correct answer: D. scattering of light by air molecules

   Air molecules scatter short (blue) wavelengths much more than long (red) ones, so blue light reaches us from all over the sky.

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2. 2

   Hypermetropia (long-sightedness) is corrected with a:

   Aconvex lensBcylindrical lensCplane glassDconcave lens

   Correct answer: A. convex lens

   A long-sighted eye cannot focus on near objects; a converging (convex) lens helps. Myopia is corrected with a concave lens.

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3. 3

   In which unit is the power of a lens expressed?

   ACandelaBDioptreCWattDLux

   Correct answer: B. Dioptre

   Power in dioptres = 1 ÷ focal length in metres; a convex lens has positive power.

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4. 4

   The speed of sound in air at room temperature is about:

   A3,400 m/sB340 m/sC3 × 10⁸ m/sD34 m/s

   Correct answer: B. 340 m/s

   Sound travels at roughly 340 m/s in air; 3 × 10⁸ m/s is the speed of light.

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5. 5

   An echo is produced by the:

   Areflection of soundBinterference of lightCrefraction of soundDabsorption of sound

   Correct answer: A. reflection of sound

   An echo is sound reflected back from a surface; to be heard separately, the reflector must be at least about 17 m away.

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6. 6

   Ultrasound is sound with a frequency:

   Abelow 20 HzBexactly 50 HzCabove 20,000 HzDbetween 20 Hz and 20,000 Hz

   Correct answer: C. above 20,000 Hz

   Humans hear about 20 Hz to 20 kHz; above that is ultrasound and below 20 Hz is infrasound.

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7. 7

   Bats find their way in the dark using:

   Aultrasound echoesBinfrared lightCmagnetic fieldsDinfrasound

   Correct answer: A. ultrasound echoes

   Bats send out ultrasonic squeaks and judge distances from the echoes (echolocation).

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8. 8

   The pitch of a sound depends on its:

   Awavelength in a vacuumBspeedCfrequencyDamplitude

   Correct answer: C. frequency

   Higher frequency gives higher pitch; amplitude decides loudness.

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9. 9

   An electric fuse works on the:

   Aphotoelectric effectBheating effect of currentCmagnetic effect of currentDchemical effect of current

   Correct answer: B. heating effect of current

   Too much current heats the thin fuse wire until it melts and breaks the circuit.

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10. 10

    Electrical resistance is measured in which SI unit?

    AampereBohmCwattDvolt

    Correct answer: B. ohm

    Resistance is measured in ohms (Ω); by Ohm's law, R = V ÷ I.

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12. 11

    Potential difference between two points in a circuit is measured with a:

    AgalvanometerBammeterCvoltmeterDbarometer

    Correct answer: C. voltmeter

    A voltmeter is connected in parallel across the two points; an ammeter is connected in series to measure current.

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13. 12

    The frequency of household AC supply in India is:

    A50 HzB60 HzC100 HzD220 Hz

    Correct answer: A. 50 Hz

    India's mains supply is about 230 V at 50 Hz; the USA uses 60 Hz.

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14. 13

    A transformer is used to:

    Ameasure electric powerBchange AC into DCCstore electric chargeDincrease or decrease AC voltage

    Correct answer: D. increase or decrease AC voltage

    A transformer works by mutual induction and works only with AC; a rectifier changes AC into DC.

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15. 14

    An electric motor converts:

    Amechanical energy into electrical energyBheat into electricityClight into electricityDelectrical energy into mechanical energy

    Correct answer: D. electrical energy into mechanical energy

    A motor uses the magnetic effect of current to produce rotation; a generator does the reverse.

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16. 15

    The "unit" on an electricity bill is the:

    Avolt-ampereBwattCjouleDkilowatt-hour

    Correct answer: D. kilowatt-hour

    One unit = 1 kWh = the energy used by a 1,000 W appliance in one hour = 3.6 × 10⁶ joules.

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17. 16

    Optical fibres carry light signals using:

    AdiffractionBpolarisationCtotal internal reflectionDdispersion

    Correct answer: C. total internal reflection

    Light keeps reflecting inside the glass core, so it travels long distances with little loss.

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18. 17

    The rear-view mirror of a vehicle is a:

    Aconvex mirrorBconcave mirrorCcylindrical mirrorDplane mirror

    Correct answer: A. convex mirror

    A convex mirror gives an upright, smaller image and a wide field of view.

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19. 18

    Shaving mirrors and dentists' mirrors are usually:

    Aplane mirrorsBconvex mirrorsCtwo-way mirrorsDconcave mirrors

    Correct answer: D. concave mirrors

    When the face or tooth is close to it, a concave mirror forms an enlarged, upright image.

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20. 19

    The kinetic energy of a body of mass m moving with speed v is:

    AmvB½mv²CmghDm²v

    Correct answer: B. ½mv²

    Kinetic energy = ½mv², so doubling the speed makes it four times as large; mgh is potential energy.

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21. 20

    Why a ship floats is explained by:

    ABoyle's lawBPascal's lawCArchimedes' principleDNewton's first law

    Correct answer: C. Archimedes' principle

    A floating body displaces water whose weight equals its own weight; the upward buoyant force balances it.

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