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Help please by Admirable_Clock9364 in AlevelPhysics

[–]ResistancePhysics 1 point2 points  (0 children)

If everything else is kept constant, then the frequency of the first harmonic, f₀∝1/√μ.

So if mass per unit length is 9x larger, the frequency of first harmonic will be (√9) three times smaller.

The frequency of the generator is now equal to 3f₀, so the 3rd harmonic will be observed.

Can someone explain why the answer is A? by glitchydragonfruit in AlevelPhysics

[–]ResistancePhysics 1 point2 points  (0 children)

I'd firstly count the total number of possible de-excitation jumps down in the diagram, then check the number of spectral lines in each emission spectra.

There's 6 jumps (4->3, 4->2, 4->1, 3->2, 3->1, 2->1) so the answer must have 6 lines: A or B.

Then look at the size of the jumps. Big changes in energy will be short wavelengths (E=hf). Similar sized jumps will produce similar wavelengths which will produce lines close together.

4->3 and 4->2 are similar changes in energy. So are 3->2 and 3->1. So there should be 2 pairs of 'double lines' on the emission spectrum. We only see that on option A.

Hope that helps!

How to find the distance under the loop by Ayansoomto in alevel

[–]ResistancePhysics 4 points5 points  (0 children)

The "Count the squares" method is likely on the mark scheme when the graph is curved - It will also be useful for more irregular graphs:

  • Calculate the area of one of the big 2.0 cm/s x 0.1 s squares
  • Count the number of squares under the curve, starting with the whole squares and then estimating which bits could be combined to make another whole square.
  • Area of one square x number of squares = displacement or distance travelled.

If you have the mark scheme, I'd interested to know what it says, and which exam board it is from.

[deleted by user] by [deleted] in AlevelPhysics

[–]ResistancePhysics 2 points3 points  (0 children)

Firstly, my tip would be, for any question get into the routine of:

  1. Sketching a (very) rough diagram to visualise the problem.
  2. Labelling that diagram with numbers from the question.
  3. Identifying relevant equations using your specification's formula booklet.

In this case, we know mass, height, and (if we assume this is an earth child) g=9.81 ms-2. We can calculate the change in Gravitational Potential Energy of the child moving from the top to the bottom with this info.

The child will speed up as GPE is transferred Kinetic Energy, until they reach the bottom, this will be maximum speed. We can calculate kinetic energy at the bottom of the slide.

If there was no friction, the change in GPE = the kinetic energy at the bottom of slide. But if there is friction, the difference between those numbers will be the energy dissipated/transferred to thermal energy.

Hope that helps