Problem 36E

A particular frost-free refrigerator uses about 745 kWh of electrical energy per year. Express this amount of energy in each unit:

a. J

b. kJ

c. Cal

Solution: The spectrum of hydrogen atom has played a very important role in the development of atomic structure. It can be obtained by passing an electric discharge through the gas taken in the discharge tube under low pressure. The emitted light is analysed with the help of spectroscope. The spectrum consists of a large number of lines appearing in different regions of wavelengths. The line spectrum observed in case of hydrogen atom can be quantitatively explained using Bohr’s model. When an electron jumps from a lower orbit to a higher orbit, it absorbs energy. When the electron jumps from higher orbit to lower orbit, it emits energy. The amount of energy absorbed or emitted when an electron jumps from orbit n(initial orbi) to orbit nffinal orbit) may be given as: --------(1) Step1: a) i) A hydrogen atom in the n = 3 state will emit energy when it comes to the lower energy state, i.e., n = 2 or n = 1. Therefore, it can emit light at only two specific wavelengths- n = 3 n = 2 and n = 3 n = 1. Thus the statement is true. Step2: ii) As the value of n(principal energy level) increases, the energy value increases. Therefore, a hydrogen atom in the n = 2 state is at a higher energy than the n = 1 state. Thus the statement is false. Step3: iii) From equation (1) above, it is seen that the energy of an emitted photon equals the energy difference of the two states involved in the emission. Thus, the statement is true. Step4: b) When an electron jumps from its ground state(lower energy level) to an excited state(higher energy level), it moves farther from the nucleus and hence expands. ----------------