Question

Suppose that resistors R1 and R2 are connected in parallel to give an equivalent resistor R. If resistors R1 and R2 have tolerance of 1% each the equivalent resistor R for resistor R1 = 300 Ω and R2 = 200 Ω will have tolerance of
1. 0.5%
2. 1%
3. 1.2%
4. 2%

Answer 1

Correct Answer - Option 2 : 1%

R1 = 300 ± 1% = [297, 303]

R2 = 200 ± 1% = [198, 202]

Actual Reff \(= \frac{{{R_1} \times {R_2}}}{{{R_1} + {R_2}}} = \frac{{200 \times 300}}{{500}} = 120\)

R1 = 297, R2 = 198

Reff = 118.8

R1 = 303, R2 = 202

Reff = 121.2

⇒Reff = [118.8, 121.2]

= 120 ± 1.2 Ω 

= 120 ± 1 %

Tolerance = (118.8 - 120) / 120 = - 0.01

Tolerance = (121.2 - 120) / 120 = 0.01

⇒ Tolerance = 1 %