Q4. Assertion: the algebraic sum of the changes in potential round a closed loop in the steady DC model with no changing linked magnetic flux is zero. Reason: electric potential depends only on the location of a point. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT page 98).
Q5. A 10 V cell in series with 2 Ω and a 4 V cell in series with 1 Ω are joined in parallel, positive terminals together, across a 2 Ω resistor. Find the current in each branch.
Let V be the potential of the positive side. The junction rule gives (10 − V)/2 + (4 − V)/1 = V/2, so 9 = 2V and V = 4.5 V. The 2 Ω load carries 2.25 A, the 10 V branch 2.75 A, and the 4 V branch −0.5 A: 0.5 A flows into its positive terminal, in the charging direction (without assuming a primary cell is rechargeable) (Kirchhoff’s rules, NCERT pages 97–98).
Q6. In NCERT Example 3.5 (the cube of 1 Ω resistors on 10 V), what is the potential difference across one of the six middle edges?
Each middle edge carries I/2 = 2 A through 1 Ω, so the potential difference is 2 V (NCERT pages 98–99). The three edges of any path add 4 + 2 + 4 = 10 V, as the loop rule requires.