A small gap is left at the joints of rails in a railway track to provide space for the expansion of rail pieces when the temperature rises during summer.

Correct Option: A

A small gap is left at the joints of rails in a railway track to provide space for the expansion of rail pieces when the temperature rises during summer.

Conversion of sound energy into electrical energy is done by microphone.

Correct Option: C

Conversion of sound energy into electrical energy is done by microphone.

A dynamo converts mechanical energy into electrical energy by taking advantage of a phenomenon known as electromagnetic induction. It is an electric generator that is similar to those that provide electricity to our homes.

Correct Option: A

A dynamo converts mechanical energy into electrical energy by taking advantage of a phenomenon known as electromagnetic induction. It is an electric generator that is similar to those that provide electricity to our homes.

Assuming air to be an ideal gas, the speed of sound depends on temperature only. As air temperature increases, so does the speed of sound and vice versa. The speed of sound is completely independent of air pressure because the air pressure and air density are proportional to each other at the same temperature. The speed of sound in air depends on the density of air which in turn depends on the temperature. The speed of a sound wave in air depends upon the properties of the air, mostly the temperature, and to a lesser degree, the humidity.

Correct Option: C

Assuming air to be an ideal gas, the speed of sound depends on temperature only. As air temperature increases, so does the speed of sound and vice versa. The speed of sound is completely independent of air pressure because the air pressure and air density are proportional to each other at the same temperature. The speed of sound in air depends on the density of air which in turn depends on the temperature. The speed of a sound wave in air depends upon the properties of the air, mostly the temperature, and to a lesser degree, the humidity.

Earthquakes generate seismic waves which can be detected with a sensitive instrument called a seismograph. The earliest seismograph was invented in China A.D. 136 by a man named Choko.

Correct Option: D

Earthquakes generate seismic waves which can be detected with a sensitive instrument called a seismograph. The earliest seismograph was invented in China A.D. 136 by a man named Choko.