questions Flashcards
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.
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.
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.
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.