Four resistances carrying a current shown in Fig. `7.41` are immersed in a box containing ice at `0^(@)C`. How much ice must be put in the box every `10 min` to keep the average quantity of ice in the box constant? Latent heat of ice is `80 calg^(-1)`.

Explanation

Total resistance `R=2xx(5xx10)/(5+10)=(20)/(3)Omega`
heat produced in 5 minute `=I^(2)Rt=5xx5xx(20)/(3)xx5xx 60=50000J`
Latent heat `L=80xx4.2xx10^(3)J//kg`, mass of ice melted , `m=(H)/(L)=(50000)/(80xx4.2xx10^(3))=0.1488` kg=148.8g.