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NCERT Physics Class 12 Exemplar Chapter 3 Current Electricity Part 5
Q.21 A cell of emf E and internal resistance r is connected across an external resistance R. Plot a graph showing the variation of P. D. across R, verses R.
- When the cell of emf E and internal resistancer is connected across an external resistance R, the relationship between the voltage across R is given R by
- With the increase of R, V approaches closer to E and when E is infinite, V reduces to O.
- The graphical representation of voltage across R and the resistance R is as shown.
- This graph shows that potential difference incrc3scs with resistance after a certain value, it becomes constant equal to E.
Short Answer
Q.22 First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R. A current I is observed to flow. Then the n resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is βnβ ?
Ans:
Q.23 Let there be n resistors with and Show that when they are connected in parallel, the resultant resistance and when they are connected in series, the resultant resistance . Interpret the result physically.
And .
- In Fig. (b) , provides an equivalent route as in Fig. (a) For current. But in addition there are routes by the remaining resistors.
- Current in Fig. (b) > current in Fig. (a) . Effective Resistance in Fig. (b) Second circuit evidently affords a greater resistance.
- You can use Fig. (c) and (d) and prove
Q.24 The circuit in Figure shows two cells connected in opposition to each other. Cell is of emf and internal resistance ; the cell is of emf and internal resistance . Find the potential difference between the points A and B.
Ans:
- P. D. across
- P. D. across
- Point B is at a higher potential than A
Q.25 Two cells of same emf E but internal resistance and are connected in series to an external resistor R what should be the value of R so that the potential difference across the terminals of the first cell becomes zero?
Or
Q.26 Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1 mm. Conductor B is a hollow tube of outer diameter 2 mm and inner diameter 1 mm. Find the ratio of resistance RA to RB.