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1. 17 (a) A student uses a computer for an average of 5 hours every day. The battery supplies a current of 3.5 A to the computer. Calculate how many electrons flow through the computer’s battery in 5 hours.

b) The computer’s screen emits visible light photons with an average frequency of
5.5* 10^14 Hz. The power of the light emitted is 10 W.
Calculate the number of photons emitted per second from the computer screen.

Please can some explain their workign as well
2. (Original post by jsmith6131)
17 (a) A student uses a computer for an average of 5 hours every day. The battery supplies a current of 3.5 A to the computer. Calculate how many electrons flow through the computer’s battery in 5 hours.
What is the definition of current?

b) The computer’s screen emits visible light photons with an average frequency of
5.5* 10^14 Hz. The power of the light emitted is 10 W.
Calculate the number of photons emitted per second from the computer screen.
Each photon has some energy - how does it depend on frequency? Power is energy per second. How much energy is emitted each second? How does it depend on the number of photons emitted each second?
3. a) Current = rate of flow of charge (NOT NUMBER OF ELECTRONS)

b)
energy of each photon = 3.6 * 10^-19 J
therefore power per photon (per second) = 3.6*10^-19

10 Watts per second

Total watt / watt per photon
10 / 3.6*10^-19 = 2.78 * 10^-19

??
4. (Original post by jsmith6131)
a) Current = rate of flow of charge (NOT NUMBER OF ELECTRONS)

b)
energy of each photon = 3.6 * 10^-19 J
therefore power per photon (per second) = 3.6*10^-19

10 Watts per second

Total watt / watt per photon
10 / 3.6*10^-19 = 2.78 * 10^-19

??
If you have rate of flow of charge you can calculate the amount of charge passing in a certain amount of time, and if know the charge of an electron you can figure out how many times the charge of an electron goes into the total charge 'used'
5. Q = It
Q = 3.5 * 5 * 60 * 60
Q = 63000 C
Q/1.6*10^-19 = 3.9 * 10^23
6. (Original post by jsmith6131)
Q = It
Q = 3.5 * 5 * 60 * 60
Q = 63000 C
Q/1.6*10^-19 = 3.9 * 10^23
Correct

(Original post by jsmith6131)
b)
energy of each photon = 3.6 * 10^-19 J
therefore power per photon (per second) = 3.6*10^-19

10 Watts per second

Total watt / watt per photon
10 / 3.6*10^-19 = 2.78 * 10^-19
There is a miscalculation, but generally correct. One reservation would be that it doesn't make sense to speak about 'watts per second' (in this context). 1 watt is 1 joule per second.
7. I dont get part b at all.

P = E/t <<< so how come we are dividing power by energy?

I dont get part b at all.

P = E/t <<< so how come we are dividing power by energy?

The energy is that of a single photon. The power is total energy output per second. So the number of photons is power / energy.

Spoiler:
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The screen emits P = 10 joules per second.

On average, you have the following:
Energy is carried by photons of frequency f = 5.5 * 10^14 Hz.
The energy of a single photon is hf joules.
So photons are emitted at a rate of P / hf = 2.7 x 10^19 Hz.

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