Which one of the following statements is true?

a. neither chemical nor physical changes involve a change in appearance.
b. both chemical and physical changes can involve a change in appearance.

c. only chemical changes involve a change in appearance.

d. only physical changes involve a change in appearance.

Alinearly polarized electromagnetic wave has an average intensity of 196 w/m^2. this wave is directed towards two ideal polarizers (in real polarizers, transmission is also effected by reflection and absorption). polarizer a is oriented with its transmission axis at an angle of θ_1=20.8∘ with the incident electric field. polarizer b has its axis at an angle of θ_2=63.0∘ with the incident electric field. what is the average intensity of the wave after it passes through polarizer a? what is the average intensity of the wave after it passes through polarizer b? suppose that the two polarizers a and b are interchanged. what would the average intensity be after passing through both polarizers?

4. a 75.0 g piece of ag metal is heated to and dropped into 50.0 g of water at the final temperature of the mixture is what is the specific heat capacity of silver? 5. a 465 g chunk of iron is removed from petrucci, ralph h.. general chemistry (p. 290). pearson education. kindle edition.

Refrigerant-134a flows through a carnot heat pump cycle at 0.5 kg/s. it is known that the maximum absolute temperature in the cycle is 1.1 times the minimum absolute temperature, and the net power input to the cycle is 2.5 kw. if the refrigerant changes from a saturated vapor to a saturated liquid during the heat rejection process, determine the maximum magnitude of the enthalpy of vaporization for this process in kj/kg (with 3 significant figures).