Superposition & Stationary Waves (OCR A Level Physics)

Hydrogen atoms excited in a discharge tube only emit four different discrete wavelengths of visible photons.

Fig. 5.1 (not to scale)                                           Fig. 5.2 (not to scale)

Four first order images of the slit, one at each photon wavelength, are observed as vertical lines against the background of the plastic ruler, as shown in Fig. 5.3.

Fig. 5.3

• Describe how the information that has been given can be used to determine the wavelength of the red photons.
• Estimate the percentage uncertainty in the measured value of the wavelength.

[6]

b)

i) Show that the energy of a photon of wavelength 486 nm is 4.09 × 10^–19 J:

List the known quantities:

• Photon wavelength,  = 486 nm = 486 × 10⁻⁹ m

From the data booklet: 

• 
• Planck's constant,  = 6.63 × 10⁻³⁴ J s
• Speed of light,  = 3.00 × 10⁸ m s⁻¹

Substitute the known quantities into the equation:

• [1 mark]

Calculate the energy of the photon, :

• (as required)

ii) Draw an arrow on Fig. 5.4 to show an electron transition which would cause the emission of a photon of wavelength 486 nm:

List the known quantities:

• Energy of a photon,  = 4.09 × 10^–19 J (from part (i))

Obtain the energy levels with a difference of :

• 
• Hence the electron transitions between
  • 
  • 

A diagram that would score 2 marks should look like this:

• A vertical arrow drawn pointing downwards; [1 mark]
• The arrow points from −1.36 to −5.45; [1 mark]

[Total: 3 marks]

Fig. 17.1

The period of the wave is T.

i)

On Fig. 17.1, sketch a graph to show the variation of the displacement at time t =.

[1]

Fig. 17.2

The frequency f of the oscillations for each stationary wave is shown in Fig. 17.2.

Use Fig. 17.2 to explain how the frequency f of the sound wave depends on the wavelength .

[3]

[1]

Fig. 16.1

Coherent blue light from a laser is incident at a double-slit. The separation between the slits is 0.25 mm. A series of dark and bright lines (fringes) appear on the screen. The screen is 4.25 m from the slits.

Fig. 16.2 shows the dark and bright fringes observed on the screen.

Fig. 16.2

The pattern shown in Fig. 16.2 is drawn to scale.

wavelength = ............................ m [3]

State and explain the effect, if any, on the fringes observed on the screen.

[2]

[2]

Fig. 19.2

Explain why the output signal from the receiver fluctuates between minimum and maximum values as the receiver moves from P to Q.

[3]