Malus and Brewster

In EM-wave, E-field oscillates perpendicular to the propagation.

• Unpolarized wave: E-field oscillates in all possible directions on the plane


• Polarized wave: E-field oscillates along a line (aka linearly or plane polarized)

Polarizer transmits the the component of E-field parallel to its transmission axis. And cuts 50 % of the intensity of unpolarized light.

Malus law: Set the transmission axes of the first and the third polarizers perpendicular to each other. How would you orientate the middle polarizer to have maximum intensity received in the detector? Can you proof it theoretically?

Brewster law: Reflected light is completely polarized if there a right angle between reflected and refracted components. Otherwise it is partially polarized. Rotate the View Angle and take a look to the two components.

Resolution and Rayleigh

Resolution is the minimum separation of two distinguishable objects in an image. Due to wave nature of light, the images get meshed i.e. the diffraction patterns overlap.

Rayleigh criterion: The two images are resolvable if the center peak of one image is exactly over the first minimum of an another image.

Take a look to see how different variables affect to the resolution of optical device.

On a dark night you look down a deserted road and see a distant light growing brighter, brighter... Then it splits into two distinct points of light: the headlights of a car coming towards you! At that moment, how far away is the car?

PRE-IB home practical on thermophysics

Cooling rate

The aim of the practical is to investigate the cooling rate of the tea sample. The temperature (T) of the sample is measured as a function of time (t).

1. The measurement is done at room temperature. Use boiling water to have high initial temperature.
· Take two identical mugs and fill them with 1 dl and 2 dl of tea.
· Read the temperature of the samples every 5 min for over an hour time interval.
· Remember to read the room temperature.

2. Repeat the two measurements outside. Remember to have the same mug and the same initial temperature. Measure the outside temperature.

3. Plot all the data in one (t,T) -system of coordinates.
· Indicate the different data sets
· Draw lines of best fit by eye to the data sets
· Determine the average cooling rate (unit: °Cs-1) for each sample
· Determine the cooling rate at the time t = 0,5 h for both 2 dl samples.

4. Answer briefly:
· How does the cooling rate change as a function of time?
· How does the mass affect on the cooling rate?
· How does the outside temperature affect on the cooling rate?
· Can you explain the shape of the curve?
· Are there any other variables affecting to the cooling rate? How would you investigate their contribution?

Single slit diffraction

Diffraction takes place at any slit, obstacle, edge... Relative size of aperture to the wavelength defines the amount of diffraction in a slit.

The diffraction pattern consist of bright and dark fringes:

• Bright due to constructive interference: path difference between the waves is a multiple of wavelength (central fringe, exactly zero)


• Dark due to destructive interference: path difference between the waves is a multiple of half wavelength (first dark fringes around central fringe, exactly one half of a wavelength).

Check the relationship between the location of dark fringes, wavelength and aperture.