Two elements A and B with atomic numbers Z_A and Z_B are used to produce characteristic X-rays with frequencies v_A and v_B respectively. If Z_A : Z_B = 1 : 2, then v_A : v_B will be

• $1 : \sqrt{2}$

• 1 : 8

• 4 : 1

• 1 : 4

In which of the following phenomena, the heat waves travel along straight lines with the speed of light ?

• Thermal conduction

• Forced convection

• Natural convection

• Thermal radiation

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

• the frequency of the microwave must match the resonant frequency of the water molecules

• the frequency of the microwave has no relation with natural frequency of water molecules

• microwave are heat waves, so always produce heating

• infrared waves produce heating in a microwave oven

• a < b, b > c
• a > b, b > c
• a > b, b < c
• a < b, b < c

The energy of gamma (γ) ray photon is E_γ and that of an X-ray photon is E_x. If the visible light photon has an energy of E_v, then we can say that

• E_X > E_γ > E_v

• E_γ > E_v > E_X

• E_γ > E_X > E_v

• E_X > E_v > Eγ