Question

1. in photoelectricity, the number of electrons emitted per second from a metallic surface is proportional to the

a. work function of the metal.
b. frequency of the incident radiation.
c. energy of the incident radiation.
d. intensity of the incident radiation.

1. a radio station broadcast covers a distance of 3.27 m away at a nearby stadium. at what frequency was the radio wave transmitted? c = 3.0 × 10⁸ ms⁻¹

a. 92.5 mhz
b. 98.1 mhz
c. 100.9 mhz
d. 91.7 mhz

1. when two substances are placed in contact with each other and no net exchange of thermal energy occurs between them during the contact, the substances must have the same

a. heat of fusion.
b. heat of vaporization.
c. temperature.
d. specific heat capacity.

1. hot ware of mass, x g is added to water of mass, \\(\frac{x}{2}\\) g at 20 °c. if the temperature of the mixture is 50 °c, calculate the initial temperature of the hot water.

a. 72 °c
b. 65 °c
c. 86 °c
d. 55 °c

1. which of the following statements about x-rays is correct? they

a. have very low frequency.
b. have long wave length.
c. cause certain materials to fluorescence.
d. are affected by electric fields.

Explanation:

Question 29

In the photoelectric effect, the number of electrons emitted per second (photocurrent) is proportional to the intensity of the incident radiation. The work function relates to the threshold frequency, frequency relates to the kinetic energy of emitted electrons, and energy of incident radiation (per photon) relates to electron energy, not the number of electrons emitted per second. So the correct option is D.

Step1: Recall the wave equation

The wave equation is \( c=\lambda f \), where \( c \) is the speed of light, \( \lambda \) is the wavelength, and \( f \) is the frequency. We need to find \( f \), so we can rearrange the formula to \( f = \frac{c}{\lambda} \).

Step2: Substitute the given values

Given \( c = 3.0\times10^{8}\, \text{m/s} \) and \( \lambda = 3.27\, \text{m} \). Substituting these values into the formula: \( f=\frac{3.0\times 10^{8}}{3.27}\approx9.17\times 10^{7}\, \text{Hz} \). Convert to MHz (since \( 1\, \text{MHz}=10^{6}\, \text{Hz} \)): \( 9.17\times 10^{7}\, \text{Hz}=91.7\, \text{MHz} \).

When two substances are in thermal equilibrium (no net exchange of thermal energy), they have the same temperature. Heat of fusion is related to phase change (solid - liquid), heat of vaporization to liquid - gas phase change, and specific heat capacity is the heat required to change temperature per unit mass. So the correct option is C.

Answer:

D. intensity of the incident radiation.

Question 30