Home › Tamil Nadu SSLC (Class 10) › Physics › Electricity › Two resistors give 2 ohm when joined in parallel…
Two resistors give 2 ohm when joined in parallel and 9 ohm when joined in series. What are the two resistance values?
A1 ohm and 8 ohm
B4 ohm and 5 ohm
C2 ohm and 7 ohm
D3 ohm and 6 ohm
Answer & Solution
Correct answer: D. 3 ohm and 6 ohm
1. Write the two conditions from the data given.
2. Series gives $R_1 + R_2 = 9$.
3. Parallel gives $\dfrac{R_1 R_2}{R_1 + R_2} = 2$, so $R_1 R_2 = 2 \times 9 = 18$.
4. Now find two numbers that sum to 9 and have product 18; these are 3 and 6.
5. Check: parallel $= \dfrac{3\times6}{9} = 2\,\Omega$, series $= 9\,\Omega$, both match.
6. Trap B (4,5): sum 9 but product 20, so parallel would be 2.22, not 2.
7. Trap C (2,7): product 14 gives parallel 1.56; trap D (1,8): product 8 gives parallel 0.89.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 4 Electricity "Electricity", p.64_
Related questions
A charged comb picks up small pieces of paper that carry no net charge, because the paper Compared with the tiny nucleus, the electrons around it form a cloud that is:Benjamin Franklin explained early observations by supposing that one type of charge stayedA test charge or a source charge moves, and as a result the force between them:If the two ends of a dipole can be pulled apart, induction can create charged objects withPlaced in a uniform field, such a dipole experiences a turning effect that changes its angTwo equal and opposite charges separated by a small distance form a dipole, characterised Where those lines are packed more densely, the field is: