Calculate the effective resistance of the resistors shown in this circuit diagram - Leaving Cert Physics - Question e - 2015

Substituting the values of the resistors into the formula:

$\frac{1}{R_{eff}} = \frac{1}{20} + \frac{1}{5}$

Calculating the right side, we first convert the fractions to a common denominator:

$\frac{1}{20} + \frac{1}{5} = \frac{1}{20} + \frac{4}{20} = \frac{5}{20}$

Thus, we have:

$\frac{1}{R_{eff}} = \frac{5}{20}$

To find $R_{eff}$, we take the reciprocal:

$R_{eff} = \frac{20}{5} = 4 Ω$

Therefore, the effective resistance of the resistors in the circuit is 4 Ω.