Josh did an experiment recording the changes in temperature in sand and water when exposed to a light source, and then when the light source was removed. josh noticed that the sand heated up faster than the water and then cools faster than the water. josh concludes that

Before going to solve this question first we have to understand specific heat capacity of a substance .

The specific heat of a substance is defined as amount of heat required to raise the temperature of 1 gram of substance through one degree Celsius. Let us consider a substance whose mass is m.Let Q amount of heat is given to it as a result of which its temperature is raised  from T to T'.

Hence specific heat  of a substance is calculated as-

Here c is the specific heat capacity.

The substance whose specific heat capacity is more will take more time to be heated up to a certain temperature as compared to a substance having low specific heat which is to be heated up to the same temperature.

As per the question John is experimenting on sand and water.Between sand and water,water has the specific heat 1 cal/gram per degree centigrade which is larger as compared to sand.Hence sand will be heated faster as compared to water.The substance which is heated faster will also cools faster.

From this experiment John concludes that water has more specific heat as compared to sand.

we can conclude that emissivity of sand will me more than the emissivity of water

Explanation:

As we know that here Source of light is the energy source from which energy is continuously incident on the Sand and Water

So here we know that rate of energy incident on sand and water will be from same source at same rate

Here this energy absorbed by the system is given as

so here the rate of energy absorbed is more sand than water

Also when source is off than rate of energy dissipated by sand is more than the water

So here we can conclude that emissivity of sand will me more than the emissivity of water

answer; /// the above statement is (true);