A battery of emf 100V and a resistor of resistance `10k(Omega)`are joined in series. This system is used as a source to supply current to an external resistance R. If R is not greater than `100(Omega)`, the current through it is constant up to two significant digits. Find its value, This is the basic principle of a constant-current source.

Explanation

`E = 100 volt, R' = ` 100 k Omega = 100000 Omega`,
` R=1 upto 100 `
` when no other register is added or r = 0 `
` i= E/R = 100/10000 = 0.001 Amp.`
` when r = 1`
` i= (100/100000+1) = 100/100001`
` = 0.000999A`
up to r = 100, the current does not up to
two significant digits. Thus it is proved.