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## Kalyani's Physics Flashback ### Current Electricity 25. Three cells of emf 2v, 5v and 7v are connected in parallel. The effective emf of the combination is **(iii) 7v** 26. Does current in a vacuum tube obey ohm's law? (Reply in yes or No) 27. Distinguish between potential difference an...

## Kalyani's Physics Flashback ### Current Electricity 25. Three cells of emf 2v, 5v and 7v are connected in parallel. The effective emf of the combination is **(iii) 7v** 26. Does current in a vacuum tube obey ohm's law? (Reply in yes or No) 27. Distinguish between potential difference and emf. 28. The amount of charge passing through any section of a conductor as a function of time is given by Q = 3t² + 2t + 5. Calculate the current flowing through the conductor at the end of 3 seconds. Assume charge in coulomb and time in second. 29. What is the current through the arm BD in the circuit diagram given below? Answer with reason.  30. A cell of emf E is connected across a conductor of resistance R. If the potential difference across the terminals of the conductor is found to be V, then the internal resistance of the cell is **(b) R(E-V)** 31. Electric conductivity is the reciprocal of _**resistivity**_. 32. Write the mathematical relation between electric current and current density in a conductor. Identify the symbols used. 33. A wire of uniform area of cross section a, length / and resistance R is cut at the middle into two equal parts of length l/2 each. Then the resistivity of each piece compared to that of the original becomes **(iii) unchanged** 34. Three resistances each 5Ω are connected to form a triangle. The resistance between any two terminals is _**2.5Ω**_. 35. State kirchhoff's laws as applicable to electrical networks.