when resistor of 5ohm is connected across its pd is balanced by 150 cm. when 10 ohm resistance is connected pd is balanced by 175 cm. calculate balancing length and internal resistance
Answers
r=R[l1l2−1]=2[240140−1] =2Ω
Ans : (D)
NCERT Solutions class 12 physics Current Electricity
1: The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4 , what is the maximum current that can be drawn from the battery?
2: A battery of emf 10 V and internal resistance 3 is connected resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?
3: (a) Three resistors are combined in series. What is the total resistance of the combination?
(b) If the combination is connected to a battery of emf 12 V and negligible internal resistance, obtain the potential drop across each resistor.
4. (a) Three resistors 2 Ω, 4 Ω and 5 Ω are combined in parallel. What is the total resistance of the combination?
(b) If the combination is connected to a battery of emf 20 V and negligible internal resistance, determine the current through each resistor, and the total current drawn from the battery.
5: At room temperature (27.0 °C) the resistance of a heating element is 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is ?
6: A negligibly small current is passed through a wire of length 15 m and uniform cross section 6.0 ×, and its resistance is measured to be 5.0 . What is the material at the temperature of the experiment?
8: A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds toa steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0 °C? Temperature coefficient of resistance of nichrome averaged over the temperature range involved is
9: Determine the current in each branch of the network shown in fig 3.30:10: (a) In a metre bridge [Fig. 3.27], the balance point is found to be at 39.5 cm from the end when the resistor Y is of 12.5 Ω.
(b) Determine the balance point of the bridge above if X and Y are interchanged.
(c) What happens if the galvanometer and cell are interchanged at the balance point of the bridge? Would the galvanometer show any current?
11: A storage battery of emf 8.0 V and internal resistance 0.5 is being charged by a 120 V dc supply using a series resistor of 15.5. What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?
12: In a potentiometer arrangement, a cell of emf 1.25 V gives a balance point at 35.0 cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0 cm, what is the emf of the second cell?
13: The number density of free electrons in a copper conductor estimated in Example is . How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross section of the wire is and it is carrying a current of 3.0 A.
14: The earth’s surface has a negative surface charge density of . The potential difference of 400 kV between the top of the atmosphere and the surface results (due to the low conductivity of the lower atmosphere) in a current of only 1800 A over the entire globe. If there were no mechanism of sustaining atmospheric electric field, how much time (roughly) would be required to neutralize the earth’s surface? (This never happens in practice because there is a mechanism to replenish electric charges, namely the continual thunderstorms and lightning in different part of the globe [Radius of earth =
15: (a) Six lead-acid type of secondary cells each of emf 2.0 V and internal resistance 0.015 are joined in series to provide a supply to a resistance of 8.5. What are the current drawn from the supply and its terminal voltage?
(b) A secondary cell after long use has an emf of 1.9 V and a large internal resistance of 380 Ω. What maximum current can be drawn from the cell? Could the cell drive the starting motor of a car?
16: Two wires of equal length, one of aluminum and the other of copper have the same resistance. Which of the two wires is lighter? Hence explain why aluminum wires are preferred for overhead power cables. (Al =, Cu =, Relative density of Al = 2.7, of Cu = 8.9.)
17: What conclusion can you draw from the following observations on a resistor made of alloy manganin?
CURRENT
VOLTAGE
CURRENT
VOLTAGE
0.2
3.94
3
59.2
0.4
7.87
4
78.8
0.6
11.8
5
98.6
0.8
15.7
6
118.5
1.0
19.7
7
138.2
2.0
39.7