Question

A 60 W (110 V) light bulb has a tungsten filament of diameter 0.06 mm. The resistivity of the tungsten at this temperature is 5.0 x 10^-7 Ωm. The length of the filament must be:

(ii) 0.60 m

(ii) 2.2 m

(iii) 4.6 m

(iv) 1.1 m

Answer 1

Since, the formula of electric power is that,

............................................(1)

and the formula of resistance R is that,

...............................................(2)

hence from equation (1) and (2) we can write that ,

m

hence the length of the filament is in two significant figures is 1.1 m

hence option (iv) 1.1 m is correct option.