cssa trials 2001 (1 Viewer)

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hai
iv been tryna do question 2 for the multiple choice on the cssa trials for 2001 and dont even know where to start

but.. i tried puttin the wavelength into m's, then subbed in to
c = f * wavelength

plzz im so lost

get bak to me as soon as possible
thanx a bunch

bye

 

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and question 15 too

 

[jims]

Q2: u dont need to use the wavelength. they tell u it takes 4 mins (240s) to travel from mars to earth and EMR always travels at 3x10^8 so the answer is just 3x10^8 x 240 = 7.2x10^10m (B).

Q15: this one im not to sure about...i can get their answer (B), but i get something else. anyway, they tell u its a 2 watt laser, so that is 2 Joules/sec. u calculate the energy of each photon emitted by the laser using E = hc/L (L is wavelength). then divide 2 by E and u get B, which is the answer they give. but i reckon it's all wrong because the question asked for how many photons are emitted per minute, so i think the answer is 3.6x10^20.