The volume of a sealed packet is 1 liter and its mass is 800 g. The packet is first put inside the water with a density of 1 g cm^-3 and then in another liquid B with a density of 1.5 g cm^-3. Then which one of the following statements holds true?

A simple pendulum having bob of mass m and length of string l has time period of T. If the mass of the bob is doubled and the length of the string is halved, then the time period of this pendulum will be

In which one of the following devices, the light energy is converted into the electrical energy?

SONAR is a device that is used to measure the distance of underwater objects by a ship. Which of the following types of waves does it use for this purpose?