Question

A technique of 20 mA, 400 ms produces an intensity of 200 mR. If the current is doubled and the intensity is to be held constant find the new time

Answer 1

Answer :

Given data :

Current = 20 mA

Time = 400 ms

Intensity = 200 mR (given)

We know that Intensity is the ratio of Power and Area.

So,

  

where

I = Intensity

P = Power

A = Area

In our case with current given,

Power = Current x Voltage

So,

P = i × V

then

Intensity

As, in our case, current is doubled and Intensity is same.

So, Area should be doubled or voltage should be halved or value of (V/A) should be halved.

So, It is given that Current is doubled,

As, It can be seen that, Time is inversely proportional to the current.

So, when current is doubled so the time will be halved.

So

New time = 400/2 = 200 ms

Thanks

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