draw from a V source, if the resistance of the heater coil is Ω ? (a) We are given V = V; R = Ω . From Eq. ( .
), we have the current I = V/ Ω = . A. (b) We are given, V = V, R = Ω . From Eq.
( . ), we have the current I = V/ Ω = . A. Note the difference of current drawn by an electric bulb and electric heater from the same V source!
Example . The potential difference between the terminals of an electric heater is V when it draws a current of A from the source. What current will the heater draw if the potential difference is increased to V? We are given, potential difference V = V, current I = A.
According to Ohm’s law, V = A V Ω . When the potential difference is increased to V the current is given by current = V = A V Ω . The current through the heater becomes A. Example .
Resistance of a metal wire of length m is Ω at °C. If the diameter of the wire is . mm, what will be the resistivity of the metal at that temperature? Using Table .
, predict the material of the wire. We are given the resistance R of the wire = Ω , the diameter d = . mm = × - m, and the length l of the wire = m. Therefore, from Eq.
( . ), the resistivity of the given metallic wire is ρ = ( RA/l ) = ( R π d / l ) Substitution of values in this gives ρ = . × – Ω m The resistivity of the metal at °C is . × – Ω m.
From Table . , we see that this is the resistivity of manganese. Example . A wire of given material having length