Question

a resistance of 40 ohms and one of the 60 ohm are arranged in series across 220 volt supply find the heat in joules produced by this combination of resistance in half a minute

Answer 1

Resistors are arranged in series so,
R1+R2=60+40=100ohm
I=V/R
I=220/100=2.2A
Time=Half a minute=30 sec
H=I^Rt
H=2.2×2.2×100×30

Answer 2

Let R1 = 40 ohm

R2 = 60 ohm

A/c to question ,

R1 and R2 are in series combination,

so, equivalent Resistance (Req) = R1 + R2

Req = 40 + 60 = 100 ohm

now ,

we know ,

Heat = I²Rt

also , V = IR ( according to ohm' s law )

Heat = (V/R)² ×R × t

= V²× t/R

here,

Req = R = 100 ohm

V = 220 volt

t = 30 sec

then,

Heat = (220)² × 30/100 Joule

= 48400 × 30/100 Joule

= 484 × 30 Joule

= 14520 Joule

hence, heat = 14520 Joule