MCQ-2

6) In which of the following devices, the eddy current effect is not used?

   (1)   Induction furnace

   (2)  Magnetic braking in train

   (3)  Electromagnet

  (4)  Electric heater

EXPLANATION:

• Electric heater does not involve Eddy currents. 
• It uses Joule's heating effect.

7) A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5 × 10–2 N/m. The pressure inside the bubble equals at a point Zo below the free surface of water in a container. Taking g = 10 m/s2, density of water =103 kg/m3, the value of Zo is :

   (1)  100 cm

   (2)  10 cm

  (3)  1 cm

   (4)  0.5 cm

EXPLANATION:

8) Which colour of the light has the longest wavelength?

  (1)  Red

   (2)  Blue

   (3)  Green

   (4)  Violet

EXPLANATION: 

•     Red has the longest wavelength.
•     From VIBGYOR - R (red) has the longest and V(violet) has the shortest.

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9) A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has speed of 20 cm/s. How much work is needed to stop it?

  (1)  3 J

   (2)  30 kJ

   (3)  2 J

   (4)  1 J

EXPLANATION:

          

10) The displacement of a particle executing simple harmonic motion is given by

 

Then the amplitude of its oscillation is given by :

EXPLANATION: