Question

How to determine the equivalent resistance of two resistors when connected in series?

Answer 1

add both the resistor value to get the total resistance.

Answer 2

Hi !

Let the resistances of the resistors be "R₁" and "R₂".
Let the total resistance be "R"

The current , I ,  passing through each of them is same.

But potential difference (p.d) across the two points of both the resistors is different

Let the p.d across R₁ be "V₁" and p.d across R₂ be "V₂"

Therefore , total p.d = V
V = V₁ + V₂

We know that , by Ohm's law :-
V = IR

So ,

V₁ = IR₁
V₂  = IR₂

we know that V = V₁ + V₂

so , 

IR = IR₁ + IR₂

Dividing throughout by "I"

R = R₁ + R₂

Hence , when resistors are connected in series , their total resistance is given by sum of the resistances of the resistors