Assertion (A): Snow is better insulator than ice.
Reason (R): Snow contain air packet and air is bad conductor of heat.
Snow traps air, and air is a very poor conductor of heat. Therefore, snow acts as a better insulator than solid ice. Both assertion and reason are true, and the reason correctly explains the assertion.
Assertion (A): Specific heat for melting Ice is infinite.
Reason (R): In isothermal process specific heat of substance is infinite.
Specific heat is defined as \(c = \frac{Q}{m \Delta T}\). During melting (a phase change), the temperature \(\Delta T\) remains constant, meaning \(\Delta T = 0\). Hence, the specific heat \(c\) becomes infinite. Both assertion and reason are true, and the reason explains the assertion.
Assertion (A): For small temperature difference between body and surrounding, the rate of cooling directly proportional to the difference in temperature, known as Newton’s law of cooling.
Reason (R): Newton’s law of cooling is valid for heat transfer by radiation mode only.
Assertion (A) correctly states Newton's law of cooling. Reason (R) is false; Newton's law of cooling is primarily derived from convection, and it is a good approximation for small temperature differences involving conduction and convection, not exclusively radiation.
Assertion (A): Woolen clothes keep the body warm in winter.
Reason (R): Woolen fibres enclose a large amount of air in them & both air and wool are the bad conductors of heat.
Woolen clothes trap air, which is a poor conductor of heat, reducing heat loss from the body. Wool itself is also a poor conductor. Both A and R are true, and R explains A.
Assertion (A): Salt is mixed with ice in an ice-cream box.
Reason (R): Salt lowers the temperature of ice.
Adding salt to ice creates a freezing mixture by lowering the freezing point of water (freezing point depression), allowing temperatures well below \(0^{\circ}\text{C}\). Both A and R are true, and R explains A.
Assertion (A): Snow is better insulator than ice.
Reason (R): Snow contain air packet and air is bad conductor of heat.
Snow traps air, making it a poor conductor of heat. Air is a bad conductor, hence snow acts as a better insulator than solid ice.
Assertion (A): Specific heat for melting Ice is infinite.
Reason (R): In isothermal process specific heat of substance is infinite.
Specific heat is \(C = \frac{Q}{m \Delta T}\). During melting, \(\Delta T = 0\), so \(C\) is infinite. Melting is an isothermal process, so both A and R are true and R explains A.
Assertion (A): For small temperature difference between body and surrounding, the rate of cooling directly proportional to the difference in temperature, known as Newton’s law of cooling.
Reason (R): Newton’s law of cooling is valid for heat transfer by radiation mode only.
Assertion (A) is the correct statement of Newton's Law of Cooling. Reason (R) is false, as the law applies to convection and can be approximated from radiation for small temperature differences, not exclusively for radiation.
Assertion (A): Two bodies at different temperatures, if brought in contact do not necessary settle to the mean temperature.
Reason (R): The two bodies may have different thermal capacities.
The final temperature of two bodies in contact depends on their thermal capacities \(m\times c\). If capacities are unequal, the final temperature will not be the mean. Both A and R are true, and R explains A.
Assertion (A): During phase change temperature of the substance remains constant.
Reason (R): Internal energy of the substance during change of phase remains constant.
Assertion (A) is true; temperature is constant during phase change. Reason (R) is false; internal energy changes as latent heat is absorbed/released to alter molecular potential energy.