Assertion (A): On the sea shore, cool breeze flows in the evening.
Reason (R): Convection currents are set up from sea to the land since land cools slower than water.
Land heats and cools faster than water. In the evening, land is cooler than the sea. This causes a breeze from land to sea (land breeze), not sea to land. Thus, A is true but R is false.
Assertion (A): Two thin blankets put together are less warmer than a single blanket of double the thickness.
Reason (R): Thickness increases because of vacuum layer enclosed between the two blankets.
Two thin blankets are warmer than one thick one due to trapped air layers acting as insulation. No vacuum forms. Both assertion and reason are incorrect.
Assertion (A): Density of humid air is less then density of dry air at the same temperature and pressure.
Reason (R): Mass of humid air is more than mass of dry air.
Water vapor \( H_2 O \) has a lower molar mass (approx. \(18 g/mol\) than nitrogen \( 28 g/mol\) and oxygen (\32 g/mol). Thus, replacing dry air molecules with \( H_2 O\) makes humid air less dense. Reason (R) is incorrect.
Assertion (A): Temperature near the sea-coast are moderate.
Reason (R): Water has a high thermal conductivity.
Coastal temperatures are moderate because water has a high specific heat capacity, absorbing and releasing large amounts of heat without significant temperature change.
Water's thermal conductivity is not high. Thus, R is false.
Assertion (A): Bodies radiate heat at all temperature.
Reason (R): Rate of radiation of heat is proportional to the fourth power of absolute temperature.
All bodies above 0 K radiate thermal energy. The Stefan-Boltzmann law states that the rate of radiation P is proportional to the fourth power of absolute temperature \(T^4\), i.e., \(P \propto T^4\). This law confirms that radiation occurs at any temperature above absolute zero and quantifies it. Thus, R explains A.
Assertion (A): For an ideal black body, both absorption coefficient and reflection coefficient are one.
Reason (R): Perfect absorbers are perfect reflectors.
A black body is defined as a perfect absorber (absorption coefficient = 1) and a perfect emitter, but it reflects no radiation (reflection coefficient = \(0\)).
Perfect absorbers are the opposite of perfect reflectors. Both Assertion (A) and Reason (R) are false.
Assertion (A): Heat radiations and light have identical properties.
Reason (R): A cold body does not radiate heat to the hotter surroundings.
Heat radiation (infrared) and visible light are both forms of electromagnetic waves, sharing properties like speed, reflection, and refraction. All bodies above 0 K radiate heat. A colder body radiates heat but receives more from hotter surroundings, leading to net heat gain. Thus, R is false.
Assertion (A): An ice skater can slide over ice smoothly if the skate blades are sharp.
Reason (R): Melting point of ice decreases with increase in pressure.
Sharp blades increase pressure, lowering ice's melting point (regelation). A thin water layer forms, reducing friction, allowing smooth sliding. Thus, R correctly explains A.
Assertion (A): A body with large reflectivity is a poor emitter of heat radiations.
Reason (R): A body with large reflectivity is a poor absorber of heat.
Kirchhoff's law states that a good absorber is also a good emitter. A body with large reflectivity (R) is a poor absorber (A), since A = 1 - R (assuming no transmission). Therefore, a poor absorber is a poor emitter. Both Assertion (A) and Reason (R) are true, and (R) correctly explains (A).
Assertion (A): If temperature of any body is increased by \(10\%\), then there will be \(40\%\) increase in amount of radiation from its surface.
Reason (R): Equation \(\frac{\Delta E}{E} = 4 \frac{\Delta T}{T}\) also the for large percentage increase where \(E \propto T^4\).
According to the Stefan-Boltzmann law, `\(E \propto T^4\)`. If `\(T\)` increases by `\(10\%\)`, the new temperature `\(T' = 1.1T\)`. Then `\(E' \propto (1.1T)^4 = 1.4641T^4\)`. The percentage increase is `\(46.41\%\)`. So, Assertion (A) is false. The approximation `\(frac{\Delta E}{E} = 4 \frac{\Delta T}{T}\)` is valid only for small percentage changes in temperature, not for 'large' changes like `\(10\%\)`. Therefore, Reason (R) is also false.