Physics Question

Question

Scientists have recently developed a powerful pulse laser for research materials. Find its energy output in watts for each of the ff. pulse conditions. (a.) 20 J in 10 psec, (b.) 200J in 35 nsec, (c) 800J in 1 msec ,(d.) At its peak pulse, it will produce 10 terawatts (TW) for a period of 10 psec. Find its discharge in Joules.

Find the solution given that the answer is provided

a.) 20TW

b.) 7.72 GW

c.) 800 kW

d.) 100J

Answer 1

This question asks you to turn an energy measurement in Joules (J) and a time measurement in seconds (s) and convert it to a unit of power, Watts (W).

First, we must understand how we get 1 Watt, 1 Watt is 1 Joule of Energy output in 1 Second. In math terms, this is Joules per second or J/s. A way to conceptually understand watts is how quickly or slowly energy is being provided to a particular object. An object with high wattage will consume huge amounts of energy quickly, like a microwave. A standard LED lightbulb will have a much lower wattage, since it consumes the energy much more slowly.

Now we also need to understand metric prefixes, prefixes can make the unit much bigger or smaller depending on the prefix. Lowercase prefixes usually make the unit smaller and uppercase prefixes make the unit bigger. You can easily find a full table of metric prefixes with a quick google search.

For a)

20 J has no prefix, but 10 psec can also be written a 10 picoseconds or 10^-12 seconds.

Since 10^-12 seconds is a very small number, if we divide by that we will get a very big number.

So if we divide the 20 J by 10x10^-12 seconds (20 J / (10x10^-12)), we will 20 x 10^12 seconds.

The prefix for 10^12 is Tera or T, which will give us the answer 20 TW or 20 x 10^12 Watts.

For b)

200 J has no prefix

35 nsec can be written as 35 nanoseconds or 35 x 10^-9 seconds

Using the power equation: 200 J / 35^10-9 seconds which gives you 5,714,285,714.2857142857 or 5.71 x 10^9 assuming two significant figures.

10^9 can be replaced with the giga (G) prefix, so this can be 5.71 GW (not sure how you got 7.72 GW)

For c)

800 J has no prefix

1 msec can also be written as 1 millisecond or 1 x 10^-3 seconds

800J / 1x10^-3 seconds = 800,000 W or 800 x 10^3 W. 10^3 is kilo or k so can also write this as 800 kW

for d)

10 Terawatts or 10 x 10^12 Watts

10 psec or 10 pico seconds or 10 x 10^-12 seconds

Here we will have to rearrange the power equation to solve for joules.

If W = J / s then J = W * s

10x10^12 Watts *10x10^-12 seconds = 100 J