Question : Two wires made of the same material but of different diameters are connected in series in a circuit. The current flows in the combination of wires. When current flows from the same wire with larger diameter to the one with the smaller diameter then drift velocity of the electrons
(i) will decrease
(ii) will increase
(iii) remains same
(iv) first will increase and after sometimes decrease
Doubt by Ridhi
Solution :
We know
I=neVdA
I=neVd[πr²]
I=neVd[π(d/2)²]
I=neVdπ²d²/4
4I/neπ²d²=Vd
Vd=4I/neπ²d²
Since the wires are connected in series so current (I) will remain same. Material of two wires are same so number density (n) will be same. Elementary charge (e) and π² are pure constants.
Vd∝1/d²
I=neVdA
I=neVd[πr²]
I=neVd[π(d/2)²]
I=neVdπ²d²/4
4I/neπ²d²=Vd
Vd=4I/neπ²d²
Since the wires are connected in series so current (I) will remain same. Material of two wires are same so number density (n) will be same. Elementary charge (e) and π² are pure constants.
Vd∝1/d²
So when diameter (d) decreases then drift velocity (Vd) will increases.
Hence, (ii) will increase, is the correct option.
