Three resistors 1 Ω, 2 Ω and 3 Ω are conne

Subject

Physics

Class

JEE Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

21.

y = 3 sin π t2 - x4 represents an equation of a progressive wave, where t is in second and x is in metre. The distance travelled by the wave in 5 s is

  • 8 m

  • 10 m

  • 5 m

  • 32 m


22.

A cylindrical tube open at both the ends has a fundamental frequency of 390 Hz in air. If 14th of the tube is immersed vertically in water the fundamental frequency of air column is

  • 260 Hz

  • 130 Hz

  • 390 Hz

  • 520 Hz


23.

The surface temperature of the stars is determined using

  • Planck's law

  • Wien's displacement law

  • Rayleigh-Jeans law

  • Kirchhoff's law


24.

Horizontal tube of non-uniform corss-section has radii of 0.1 m and 0.05 m respectively at M and N. For a streamline flow ofl iquid the rate of liquid flow is

          

  • changing continuously with time

  • greater at M than at N

  • greater at N than at M

  • same at M and N


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25.

A direct current I flows along the length of an infinitely long straight thin walled pipe, then the magnetic field is

  • uniform throughout the pipe but not zero

  • zero only along the axis of the pipe

  • zero at any point inside the pipe

  • maximum at the centre and minimum at the edge


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26.

Three resistors 1 Ω, 2 Ω and 3 Ω are connected to form a triangle. Across 3 Ω res1stor a 3 V battery is connected. The current through 3 Ω resistor is

  • 0.75 A

  • 1 A

  • 2 A

  • 1.5 A


B.

1 A

Required arrangement is shown in figure.

          

The equivalent circuit will look like (since the two resistances of 1 Ω and 2 Ω  are in series, which form 3 Ω which is in parallel with 3 Ω resistance).

                 

Therefore, the effective resistance is

1 + 2 × 31 + 2 + 3 = 32 Ω

                       

                  

∴ Current in the circuit,

I = 33/2 = 2 A

∴ Current in 3 Ω resistor = I2 = 1 A


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27.

Ferromagnetic materials used in a transformer must have

  • low permeability and high hysterisis loss

  • high permeability and low hysterisis loss

  • high permeability and high hysterisis loss

  • low permeability and low hysterisis loss


28.

The accurate measurement of emf can be obtained using

  • multimeter

  • voltmeter

  • voltameter

  • potentiometer


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29.

An electric heater rated 220 V and 550 W is connected to AC mains. The current drawn by it is

  • 0.8 A

  • 2.5 A

  • 0.4 A

  • 1.25 A


30.

In fog, photographs of the objects taken with infrared radiations are more clear than those obtained during visible light because

  • I-R radiation has lesser wavelength than visible radiation

  • scattering of I-R light is more than visible light

  • the intensity of I-R light from the object is less

  • scattering of I-R light is less than visible light


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