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1
Q

A student carries out an investigation to determine how the resistance of a metal varies with temperature.

The resistor is made from a coil of wire. It is placed in a beaker of hot water.

The resistance is measured for different temperatures of the water as it cools.

  • What are two precautions the student should take to ensure accurate results?
A
  • Read the temperature at eye level to avoid parallax errors.
  • Ensure that there is a small current through the resistor so that there is not an additional heating effect which would make the results inaccurate.
  • Stir the water so that the results are not affected by differences in temperature.
  • Switch off between readings so that there is no additional heating effect.
  • Check the meter for zero errors by connecting a lead across its terminals so that there is no systematic error in the measurements of the resistance.
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2
Q

Explain, in terms of the structure of the metal, why resistance increases with temperature.

A
  • At higher temperatures, the vibrations of the lattice ions increase.
  • For the same current, the electrons will collide more frequently with the lattice ions.
  • More energy is dissipated by the electrons, so for a constant I there is a greater voltage.
  • Since V increases and R=V/I, R will increase with temperature.
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3
Q

Why are there colours present when white light is reflected off a CD?

A
  • Diffraction occurs when light is reflected from the CD surface.
  • The rings on the surface of the CD act as individual diffraction centres.
    • Light hits them and is scattered in all directions.
  • The diffracted light waves interfere with one another.
  • When the path difference is an integer number of λ, there is 100% constructive interference.
  • White light is a mixture of wavelengths.
  • Each λ of light reinforces in a different direction.
    • This creates a colour spectrum.
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4
Q

What happens to these properties of a ray of light when it strikes a prism?

frequency

wavelength

speed

A
  • The frequency is unaltered.
  • The wavelength decreases.
  • The speed decreases.
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