29. 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.

30. 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 m s⁻¹
a. 92.5 mhz
b. 98.1 mhz
c. 100.9 mhz
d. 91.7 mhz

31. 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.

32. hot ware of mass, x g is added to water of mass, 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

33. 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.

Question

29. 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.

30. 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 m s⁻¹
a. 92.5 mhz
b. 98.1 mhz
c. 100.9 mhz
d. 91.7 mhz

31. 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.

32. hot ware of mass, x g is added to water of mass, 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

33. 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.

Accepted Answer

### Question 29
# Brief Explanations:
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 (if above threshold) relates to electron energy, not the number emitted. So the number of electrons emitted per second depends on intensity.
# Answer:
D. intensity of the incident radiation.

### Question 30
# Explanation:
## 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 values
Given $ c = 3.0\times10^{8}\, \text{m/s} $ and $ \lambda = 3.27\, \text{m} $ (assuming the distance is the wavelength, as radio waves are electromagnetic waves and the broadcast distance here might be the wavelength, though the unit seems large, but following the problem). Then $ f=\frac{3.0\times 10^{8}}{3.27}\approx9.17\times 10^{7}\, \text{Hz}=91.7\, \text{MHz} $.
# Answer:
D. 91.7 MHz

### Question 31
# Brief Explanations:
When two substances are in thermal equilibrium (no net heat exchange), they have the same temperature. Heat of fusion is for phase change (solid - liquid), heat of vaporization for liquid - gas, and specific heat capacity is about heat required to change temperature, but thermal equilibrium is about same temperature.
# Answer:
C. temperature.

### Question 32
# Explanation:
## Step1: Use the principle of calorimetry
The heat lost by hot water equals the heat gained by cold water. The formula is $ m_hc\Delta T_h=m_cc\Delta T_c $, where $ m_h $ is mass of hot water, $ m_c $ is mass of cold water, $ c $ is specific heat capacity (same for water, so cancels out), $ \Delta T_h $ is change in temperature of hot water, $ \Delta T_c $ is change in temperature of cold water.
## Step2: Define variables
Let initial temperature of hot water be $ T $. Mass of hot water $ m_h = X \, \text{g} $, mass of cold water $ m_c=\frac{X}{2}\, \text{g} $, initial temperature of cold water $ T_c = 20^{\circ}\text{C} $, final temperature $ T_f = 50^{\circ}\text{C} $.
## Step3: Write heat equations
Heat lost by hot water: $ Q_h=X\times c\times(T - 50) $
Heat gained by cold water: $ Q_c=\frac{X}{2}\times c\times(50 - 20) $
Since $ Q_h = Q_c $, $ Xc(T - 50)=\frac{X}{2}c(30) $
## Step4: Solve for T
Cancel $ Xc $ from both sides: $ T - 50=\frac{1}{2}\times30 = 15 $
So $ T=50 + 15=65^{\circ}\text{C} $? Wait, no, wait: Wait, $ \frac{X}{2}\times(50 - 20)=\frac{X}{2}\times30 = 15X $
And $ X\times(T - 50)=15X $, divide both sides by X: $ T - 50 = 15 $? No, wait, maybe I made a mistake. Wait, the cold water is heated from 20 to 50, so $ \Delta T_c=30 $, hot water is cooled from T to 50, $ \Delta T_h=T - 50 $.
So $ m_hc\Delta T_h=m_cc\Delta T_c $
$ X\times c\times(T - 50)=\frac{X}{2}\times c\times30 $
Divide both sides by $ Xc $: $ T - 50=\frac{30}{2}=15 $
So $ T = 50+15 = 65^{\circ}\text{C} $? But wait, the options have 65°C as option B. Wait, but let's check again. Wait, maybe the mass of hot water is X, cold water is X/2. So heat gained by cold water: $ m_c\times c\times(50 - 20)=\frac{X}{2}\times c\times30 = 15Xc $
Heat lost by hot water: $ X\times c\times(T - 50) $
Set equal: $ Xc(T - 50)=15Xc $
Cancel Xc: $ T - 50 = 15 $ → $ T = 65^{\circ}\text{C} $
# Answer:
B. 65 °C

### Question 33
# Brief Explanations:
X - rays have high frequency and short wavelength (so A and B are wrong). X - rays are electromagnetic waves, so they are not affected by electric fields (D is wrong). X - rays can cause certain materials to fluoresce (e.g., in X - ray imaging, some screens fluoresce when hit by X - rays).
# Answer:
C. cause certain materials to fluorescence.

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QUESTION IMAGE

Question

Explanation:

Question 29

Step1: Recall the wave equation

Step2: Substitute the values

Answer:

Question 30