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If you inhale some helium your voice changes so that you speak like a smurf. Hydrogen has the same effect (watch out smokers!) but it is also possible to obtain the voice of Darth Vader in this way. The most famous substance for this is sulfur hexafluoride. What causes the voice to change? Make also a quantitative guess.

When you stand in an enclosed space and play a right tone, you can face its resonance frequency. As the resonance frequency depends on the size of the resonator, it can thence be determined. Choose an appropriate room (ideally, a small one with empty walls – e.g. bathroom), measure the frequency and contrast the results.

Buy a standard glass bottle from bier of mineral water and find out, how the pitch of the tone depends on the water level inside the bottle, when you blow over the neck of the bottle.

Estimate, what energy is absorbed by the body of visitor on a rock concert. Give reasons for your answer.

An rich space-tourist has payed for a trip to the deep space. The Racket flies from the Earth and is accelerating with constant acceleration $a$, which can be verified by dropping a small ball. He is quite bored and therefore is watching disappearing Earth through the back window. After some time (how long it will take?) he starts to see, that something is not right. The Earth is not getting much smaller, and he deduces, that the space ship is slowing down, which does not correspond with the constant acceleration of $a$. However the tourist is not as good physicist and goes to file complain with captain. What should the captain to tell him?

Assume, that the tourist see whole electromagnetic spectrum and will survive the observation.

• What shape of interference pattern would you expect in following two configurations? Find the equations of curves of maximum intensity and try to plot some of them.

• Show, how the experiment should end, if the light behaves according to Newton assumptions. Do consider different angle of incidence at different places on the screen.

• Using quantum-mechanical description find resolution, which should have get Jöhnsson by using 4 slits (4 parallel orifices in distance $b$ between neighbouring slits. Plot representative part of the graph and comment advantages of higher number of orifices.

Recently there was a TV document about the eruption of Krakatoa volcano in August 1883. Remarkably the noise of eruption deafened for while people in distance 50 km from volcano. The sound of eruption was heard as distant thunder in town Alice Springs in Central Australia (approx 5 000 km from the volcano).

What was the value of acoustic pressure in dB at the place of eruption?Can we assume, that the decrease of intensity follows inverse square law? Or should we define a different rule in this case?

In this problem question think about and animal, which communicate at radio frequency (10 Hz –100 MHz). Suggest an biological equivalent of necessary radio-electronic components.

The pianist falls from the skyscraper. During the fall he is playing tone A on piano. Exactly $k$ floor lower is window cleaning man. What is value $k$, if the last thing the window cleaning man heard is tone Ais (half-tone higher then A)? Speed of sound is 347 m\cdot s^{ − 1}, height of one floor is 3,1 m.

Explain, why is it possible to 'over-blow' (play one octave higher than normally) a flute, and it is not possible with clarinet.