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# Electrical Power Watch

1. 200 pulses --- 1s
so 1pulse--- 5ms
2ms generates 15A
so 5ms generates 37.5A
P=VI
=220*37.5
=7500W
(which is not even in the options!)
Thanks for any help in advance!
2. (Original post by 123PC)

200 pulses --- 1s
so 1pulse--- 5ms
2ms generates 15A
so 5ms generates 37.5A
P=VI
=220*37.5
=7500W
(which is not even in the options!)
Thanks for any help in advance!
Here's how I would have done it:

P = VI

Therefore, the power generated by each pulse is given by
P = 220V * 15A = 3300W

Each pulse lasts for 2ms, so the energy generated by each pulse is

E = Pt = 3300W * 0.002s = 6.6J

But there are 200 pulses per second, so the energy generated per second (which is power!) is given by

P = 6.6J * 200 = 1320W

So I think the answer is 1.3kW.
3. (Original post by 123PC)

200 pulses --- 1s
so 1pulse--- 5ms
2ms generates 15A
so 5ms generates 37.5A
P=VI
=220*37.5
=7500W
(which is not even in the options!)
Thanks for any help in advance!
I see the mistake you've made - each pulse does not last 5ms, they each last 2ms, as stated in the question. What the question says is that there are 200 of these 2ms pulses in the space of a second, so they are not continuous.
4. (Original post by Ollie231213)
Here's how I would have done it:

P = VI

Therefore, the power generated by each pulse is given by
P = 220V * 15A = 3300W

Each pulse lasts for 2ms, so the energy generated by each pulse is

E = Pt = 3300W * 0.002s = 6.6J

But there are 200 pulses per second, so the energy generated per second (which is power!) is given by

P = 6.6J * 200 = 1320W

So I think the answer is 1.3kW.
5. (Original post by Ollie231213)
I see the mistake you've made - each pulse does not last 5ms, they each last 2ms, as stated in the question. What the question says is that there are 200 of these 2ms pulses in the space of a second, so they are not continuous.
Oh, I see!

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