The refractive index of water is 1.33. The direction in which a man under water should look to see the setting sun is

• 49° to the horizontal

• 90° with the vertical

• 49° to the vertical

• along the horizontal

The solar spectrum during a complete solar eclipse is

• continuous 

• emission line

• dark line

• dark band

73.

The rate of emission of a black body at 0°C is R, its rate of emission at 273°C is

• 4 R

• 8 R

• 16 R

• 32 R