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PHYA5 Option 5D: Turning Points in Physics - A2 - 20/06/2013 - Paper B

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For the last part of the first q in turning points, I couldn't show the value but I wrote that the mg weight was more than the elec force so it goes down. What do you lot think the 4 marks were ?

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I would guess 2 marks for explanation and 2 marks for showing that the charge is 1.6x10^-19

Reply 121

Technetium

Original post by HypErTwisT

Anyone want to compile a question list? and maybe some answers? Wouldn't mind knowing how I got on 2 month early xD

I have created an *Unofficial Mark Scheme* for Section B

1. (a)(i) Show that the radius of the droplet is 4.11x10^-?!(4 marks)
- Equate the weight to the viscous drag force, 4/3πrpg = 6πnrv and solve for r.

(ii) Hence calculate the mass of the oil droplet (1 mark)
- mg = 6πnrv, solve for m.

b(i) Calculate the charge on the oil droplet (3 marks)
- We were given appropriate data, equate Qv/d =mg and solve for Q.

(ii) Explain why the droplet of new mass cannot be held stationary between plates, hence show that it's charge is 1.60x10^-19 (4 marks)
- Weight exceeds force due to the electric field, the resultant force acts vertically downwards.
- Not sure about showing that the charge was 1.60x10^-19

2. (a)(i) State DeBroglies Hypothesis (2 marks)
- Matter particles have a wave-like nature; λ = h/mv where h is Planck's constant, m is the mass and v is velocity

(ii) Calculate the DeBroglie wavelength of a neutron with kinetic energy of X eV (4 marks)
- Convert the kinetic energy into J
- Find the velocity and sub into λ = h/mv

(iii) Explain why electrons with the same DeBroglie wavelength have a much greater kinetic energy than neutrons (2 marks)
- Electrons have a much smaller mass than neutrons
- Not sure about the second mark

3. (a)(i) Explain how a stationary wave pattern is formed, and how the wavelength of the waves is measured (6 marks)
- Waves produced by the transmitter are reflected by the flat metal reflector sheet
- Reflected wave overlaps with another wave produced by the transmitter; thus forming a stationary wave
- Constructive interference occurs at the nodes, destructive interference occurs at the antinodes
- When the detector is moved along a line between the transmitter and the flat metal reflector sheet minimum signal is detected at the nodes.
- Distance between two adjacent nodes = λ/2 so wavelength = 2λ.

(ii) Explain the significance of Hertz's discovery of the speed of electromagnetic waves (2 marks)
- Maxwell predicted that electromagnetic waves would travel at the speed of light
- Hertz's results confirmed this as he obtained a value of 3.0x10^8ms^-1

4. (a)(i) Calculate the speed at which a matter particle has twice it's rest mass (2 marks)
- 2mo = mo(1-v^2/c^2)^-1/2, solve for v. I think I got 2.98x10^8 ms^-1

(ii) Sketch a graph to show how the rest mass varies with speed, mark on the graph with the letter P the point at which a particle is travelling at two times it rest mass (3 marks)
- Parabola starting at 0
- Increasing curvature; and then shoots up
- Becomes asymptotic with the y-axis at around 0.90c
- Point P at 2mo, 0.88c (approximately)

(iii) By considering appropriate equations explain why a matter particle cannot travel at the speed of light (2 marks)
- As v--->c, m--->infinity.
- Kinetic energy = (m-mo)c^2
- In order for v=c, the kinetic energy would have to be infinite which is physically impossible.

Reply 122

constance2013

anyone on here taking turning points this year?

just wondering if I have to remember EVERY experiment word for word... there is....a Lot!

Reply 123

Pinkhead

Original post by constance2013

anyone on here taking turning points this year?

just wondering if I have to remember EVERY experiment word for word... there is....a Lot!

The mark schemes don't ask you to write paragraphs and paragraphs about the experiments. You just need to know how they work in general and make sure you use the correct terminology (assuming it's similar to last year's syllabus).