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PHYSICS, M3 EQ-Bank 1 MC

In a laboratory experiment, white light is passed through a prism and splits into a spectrum of colours.

What is this effect called?

  1. Diffraction
  2. Polarisation
  3. Dispersion
  4. Interference
Show Answers Only

\(A\)

Show Worked Solution
  • Dispersion occurs when different wavelengths of light refract (bend) by different amounts.
  • This separates white light into its component colours (Red, Orange, Yellow, Green, Blue, Indigo, Violet).

\(\Rightarrow A\)

PHYSICS, M3 2023 VCE 12 MC

A physics class is investigating the dispersion of white light using a lens, as shown in the diagram below.
 

The students observe the rays \(\text{K–P}\) that have been refracted by the lens.

Which one of the following correctly identifies the colour, red \(\text{(R)}\), green \(\text{(G)}\) or violet \(\text{(V)}\), of the rays \(\text{K–P}\)?
 

  \(\textbf{K}\) \(\textbf{L}\) \(\textbf{M}\) \(\textbf{N}\) \(\textbf{O}\) \(\textbf{P}\)
\(\textbf{A.}\) \(\quad \text{R}\quad \) \(\quad \text{G}\quad \) \(\quad \text{V}\quad \) \(\quad \text{V}\quad \) \(\quad \text{G}\quad \) \(\quad \text{R}\quad \)
\(\textbf{B.}\) \(\text{V}\) \(\text{G}\) \(\text{R}\) \(\text{R}\) \(\text{G}\) \(\text{V}\)
\(\textbf{C.}\) \(\text{V}\) \(\text{G}\) \(\text{R}\) \(\text{V}\) \(\text{G}\) \(\text{R}\)
\(\textbf{D.}\) \(\text{V}\) \(\text{R}\) \(\text{G}\) \(\text{G}\) \(\text{R}\) \(\text{V}\)
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\(B\)

Show Worked Solution
  • The shorter wavelengths of light (violet) experience a greater refraction so the light rays of \(P\) and \(K\) will be violet. 
  • The longer wavelength light (red) experiences the least refraction and so will be rays \(M\) and \(N\).

\(\Rightarrow B\)

PHYSICS, M3 2019 VCE 15

A student sets up an experiment involving a source of white light, a glass prism and a screen. The path of a single ray of white light when it travels through the prism and onto the screen is shown in Figure 14.
 

A spectrum of colours is observed by the student on the screen, which is positioned to the right of the prism.

  1. Name and explain the effect observed by the student.   (3 marks)

  2. Points \(\text{X}\) and \(\text{Y}\) on the diagram above represent either end of the visible spectrum observed by the student.
  3. Identify the two visible colours observed at point \(\text{X}\) and at point \(\text{Y}\).   (1 mark)

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a.   The observed effect is dispersion.

  • As light enters the glass it slows down as it is entering a denser medium.
  • As the refractive index for different wavelengths of light differs, the angle at which individual wavelengths refract differs slightly.
  • This causes the white light to split up as each wavelength refracts differently through the glass resulting in a rainbow spectrum on the screen.

 b.   Point \(X\) is red.

        Point \(Y\) is blue/purple.

Show Worked Solution

a.   The observed effect is dispersion.

  • As light enters the glass it slows down as it is entering a denser medium.
  • As the refractive index for different wavelengths of light differs, the angle at which individual wavelengths refract differs slightly.
  • This causes the white light to split up as each wavelength refracts differently through the glass resulting in a rainbow spectrum on the screen.
♦ Mean mark 53%.

b.   Point \(X\) is red.

        Point \(Y\) is blue/purple.

PHYSICS, M3 2021 VCE 15 MC

A Physics class is investigating the dispersion of white light using a triangular glass prism.

Which one of the following diagrams best shows the principle of dispersion?
  


 


 

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\(A\)

Show Worked Solution
  • Dispersion is a result of white light splitting into different colours when it is refracted.
  • Dispersion occurs during both changes in medium (i.e. from air into glass and from glass into air).
  • The shorter violet wavelengths of light experience a greater refraction than the longer wavelength red light.

\(\Rightarrow A\)

PHYSICS, M3 2022 VCE 13

A ray of green light from a light-emitting diode (LED) strikes the surface of a tank of water at an angle of 40.00° to the surface of the water, as shown in diagram below. The ray arrives at the base of the tank at point \(\text{X}\). The depth of the water in the tank is 80.00 cm. The refractive index of green LED light in water is 1.335
 

  1. Calculate the distance \(\text{OX}\). Outline your reasoning and show all your working. Give your answer in centimetres.   (4 marks)

  2. The green LED light is replaced with a narrow beam of white sunlight.
  3. Describe the colour of the light that arrives to the left of point \(\text{X}\), at point \(\text{X}\) and to the right of point \(\text{X}\).   (3 marks)
     
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a.  \(OX=56\ \text{cm}\)

b.

\begin{array} {|c|c|c|}
\hline
\rule{0pt}{2.5ex}\text{Light to the left of point X}\rule[-1ex]{0pt}{0pt} & \text{Light at point X} & \text{Light to the right of point X} \\
\hline
\rule{0pt}{2.5ex}\text{Blue/Purple}\rule[-1ex]{0pt}{0pt} & \text{Green} & \text{Red} \\ \text{(lower wavelength)} & & \text{(higher wavelength)} \\
\hline
\end{array}

Show Worked Solution

a.  \(\text{Using Snell’s Law:}\)

\(n_1 \sin \theta_1\) \(=n_2 \sin \theta_2\)  
\(\sin \theta_2\) \(=\dfrac{n_1 \sin \theta_1}{n_2}\)  
\( \theta_2\) \(= \sin^{-1}\Big{(}\dfrac{1 \times \sin 50^{\circ}}{1.335} \Big{)}=35^{\circ}\)  

 

\(\tan35^{\circ}\) \(=\dfrac{OX}{80}\)  
\(OX\) \(=80\times \tan35^{\circ}=56\ \text{cm}\)  

♦ Mean mark 48%.

b. 

\begin{array} {|c|c|c|}
\hline
\rule{0pt}{2.5ex}\text{Light to the left of point X}\rule[-1ex]{0pt}{0pt} & \text{Light at point X} & \text{Light to the right of point X} \\
\hline
\rule{0pt}{2.5ex}\text{Blue/Purple}\rule[-1ex]{0pt}{0pt} & \text{Green} & \text{Red} \\ \text{(lower wavelength)} & & \text{(higher wavelength)} \\
\hline
\end{array}

PHYSICS, M3 2014 HSC 32bi

What happens to white light when it hits a red surface?   (2 marks)

Show Answers Only
  • When white light hits a red surface, the shorter wavelengths of light are absorbed into the surface.
  • The longer red wavelengths of light are reflected off of the surface and into the eyes of the observer, hence the surface appears red.
Show Worked Solution
  • When white light hits a red surface, the shorter wavelengths of light are absorbed into the surface.
  • The longer red wavelengths of light are reflected off of the surface and into the eyes of the observer, hence the surface appears red.
♦ Mean mark 44%.