Explanation:
When resistors are connected in series, effective resistance is given by
[tex]R_{eff}=R_1+R_2+R_3+......[/tex]
Here
R₁ = 21Ω
R₂ = 58Ω
R₃ = 64Ω
a) [tex]R_{eff}=R_1+R_2+R_3\\\\R_{eff}=21+58+64\\\\R_{eff}=143\Omega[/tex]
Equivalent resistance is 143 Ω
b) We know
Potential difference = Current x Resistance
V = IR
I = 0.5 A
R = 143Ω
Substituting
V = 0.5 x 143 = 71.5 V
Potential difference is 71.5 V