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/s 2 , density of water =10 3 kg/m 3 , 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. 9) A disc of radi