Physics

# Problems

PhysicsProblems

### 21.1Planck and Quantum Nature of Light

22.

How many X-ray photons per second are created by an X-ray tube that produces a flux of X-rays having a power of 1.00 W? Assume the average energy per photon is 75.0 keV.

1. 8.33 × 1015 photons
2. 9.1 × 107 photons
3. 9.1 × 108 photons
4. 8.33 × 1013 photons
23.

What is the frequency of a photon produced in a CRT using a 25.0-kV accelerating potential? This is similar to the layout as in older color television sets.

1. 6.04 × 10−48 Hz
2. 2.77 × 10−48 Hz
3. 3.02 × 1018 Hz
4. 6.04 × 1018 Hz

### 21.2Einstein and the Photoelectric Effect

24.

What is the binding energy in eV of electrons in magnesium, if the longest-wavelength photon that can eject electrons is 337 nm?

1. 7.44 × 10−19 J
2. 7.44 × 10−49 J
3. 5.90 × 10−17 J
4. 5.90 × 10−19 J
25.

Photoelectrons from a material with a binding energy of 2.71 eV are ejected by 420-nm photons. Once ejected, how long does it take these electrons to travel 2.50 cm to a detection device?

1. 8.5 × 10−6 s
2. 3.5 × 10−7 s
3. 43.5 × 10−9 s
4. 8.5 × 10−8 s

### 21.3The Dual Nature of Light

26.

What is the momentum of a 0.0100-nm-wavelength photon that could detect details of an atom?

1. 6.626 × 10−27 kg ⋅ m/s
2. 6.626 × 10−32 kg ⋅ m/s
3. 6.626 × 10−34 kg ⋅ m/s
4. 6.626 × 10-23 kg ⋅ m/s
27.

The momentum of light is exactly reversed when reflected straight back from a mirror, assuming negligible recoil of the mirror. Thus the change in momentum is twice the initial photon momentum. Suppose light of intensity 1.00 kW/m2 reflectsfrom a mirror of area 2.00 m2 each second. Using the most general form of Newton’s second law, what is the force on the mirror?

1. 1.33 × 10-5 N
2. 1.33 × 10−6 N
3. 1.33 × 10−7 N
4. 1.33 × 10−8 N