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Fundamentals Of Physics
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Short Answer

After the switch in Fig. 27-15 is closed on point a, there is current i through resistance R. Figure 27-23 gives that current for four sets of values of R and capacitance C: (1) R0 and C0, (2) 2R0 and C0, (3) R0 and 2C0, (4) 2R0 and 2C0. Which set goes with which curve?

Nature of graph for the given conditions is as follows:

1-(d)

2 -(a)

3-(c)

4- (b)

See the step by step solution

Step by Step Solution

Step 1: Given

R0 and C02R0 and C0R0 and 2C02R0 and 2C0

Step 2: Determining the concept

Use the formula for charge in terms of capacitor and voltage and then find the current from charge, resistance, and capacitor. Further, we can use time constant values. Higher the values of RC, lower will be state of decreasing of current.

Formulae are as follow:

q=CVV=IRi=-qRC*e-tRC

Where, C is capacitance, V is potential difference, q is charge, I is current, V is voltage, R is resistance, t is time.

Step 3: Determining the nature of graph for the given conditions

Case 1) R0 and C0

First find the charge as follows:

q=CVq=C0V0

Current is given as follows:

I0=q0R0C0I0=C0V0R0C0I0=V0R0

The time constant for this case will be ,

t=R0C0

Case 2)2 R0 and C0

First find the charge as follows:

q=CVq0=C0V0

Current is given as follows:

I0=q02R0C0I0=C0V02R0C0I0=V02R0

The time constant is,

t=RC=2R0C0

Case 3) R0 and 2C0

First find the charge as follows:

q=CVq0=2C0V0

Current is given as follows:

I0=q02R0C0I0=2C0V02R0C0I0=V0R0

The time constant for this case is,

t=RC=2R0C0

Case 4) 2R0 and 2C0

First find the charge as follows:

q=CVq=2C0V0

Current is given as follows:

I0=q04R0C0I0=2C0V04R0C0I0=V02R0

The time constant for this case is,

t=RC=4R0C0

Now, if considered all cases, it can be seen that the case 1 and 3 have higher current values.

So, between these two, the value of time constant for case 3 is larger. It means this will represent the graph with more rate of decrease of current, that is, graph c.

Hence, case 1 will represent graph d.

In a similar way, case 2 will be represented by graph a and case 4 will be represented by graph b.

Hence, case 1 will represent graph d, case 2 will be represented by graph a, case 3 will be represented by graph c, case 4 will be represented by graph b.

Therefore, we can determine the nature of the graph by finding the current and time constant and then comparing them.

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