Required Practicals

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1. An investigation into the variation of the frequency of stationary waves on a string with              length, tension and mass per unit length of the string

(http://physics.appstate.edu/sites/physics.appstate.edu/files/vibrations_4_1.PNG)

  • Set up the apparatus as shown with a 1.000m string length
  • Increase frequency of signal generator from 0 until string vibrates at its fundamental frequency (ie. first harmonic)
  • Record this frequency
  • Repeat with string lengths of 0.900, 0.800, 0.700, 0.600 and 0.500m
  • Repeat experiment again and find the mean value of f for each value of l
  • plot graph of mean 1/f against l
  • Draw the line of best fit and find gradient; graph should be a straight line through the origin
  • The speed of travelling waves on string = fλ. When the string is vibrating at its fundamental mode, λ = 2l, hence λ = 2fl. The gradient is 1/fl so is given by 2/gradient in ms^-1

2. Investigation of the interference effects by Young's slit and diffraction by a diffraction            grating

Young's slit experiment:

(http://www.cyberphysics.co.uk/graphics/diagrams/waves/youngslitpattern2.png)

  • Set up the apparatus as shown in the diagram, with the laser illuminating the double slit (or use a single slit if the laser beam isn't wide enough to illuminate the double slit), and the screen a distance D of about 1 metre
  • The fringe width, w, of the interference pattern can be measured by measuring across a large number of visible fringes
  • Use a metre ruler to measure D
  • Find the slit separation, s, by reading what the manufacturer has quoted on the slide
  • Plot a graph of w against D; this should be a straight line through the origin. The gradient represents λ/s

Interference by a diffraction grating:

(http://www.saburchill.com/physics/images_practicals/Laser_diffraction_01.jpg)

  • Set up the apparatus as shown in the diagram, with the laser illuminating the diffraction grating, and the screen a distance D of about 1 metre
  • Adjust the position of the diffraction grating so that it is perpendicular to the beam of light from the laser
  • The diffraction pattern should be visible on the screen
  • The value of θ can be determined by measuring the distances y and D; the angle can then be calculated using tan^-1(y/D)
  • The formula nλ = dsinθ can be used to calculate the wavelength of light; n is the order of the diffraction pattern, d is the grating spacing = 1/ no. of lines per metre, and λ is the wavelength of light
  • The values of θ for each order, both above and below the zero order, should be measured
  • A mean value for λ can be calculated from the data

3. Determination of g by a free-fall method

  • Set up the apparatus as shown in the diagram
  • The height between the starting position of the ball bearing and the upper light gate should be kept constant so that the velocity, u, is also constant
  • Adjust the position of the lower light gate so that h is 0.500m
  • Switch on the supply to the electromagnet and hang the ball bearing from it
  • Reset the clock…

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