CBSE Guess > Papers > Important Questions > Class XII > 2011 > Physics > Physics By Mr.Ashis kumar satapathy

CBSE CLASS XII

Combination Of Resistance

A: Following questions are very short answer type. They are to be answered in one or two sentences. They may carry one mark each.

1. Why does the resistance increase in series combination?
2. Why does the resistance decrease in parallel combination?
3. Two resistors are connected in series.The equivalent resistance is R₁.When connected in parallel, equivalent resistance is R₂. V-I graphs for R₁ and R₂ are as shown in figure. State which graph is for R₁ and which is for R₂.

   

4. A uniform wire of resistance 20 Ω is cut into two equal parts. These parts are now connected in parallel. What will be the resistance of the combination?

B: The following questions are of short answer type. Each of them may carry 2 or 3 marks.

1. In the given circuit P=3 ohms, Q=2 ohms, R=6 ohms, S=4 ohms an

   

2. Three identical cells, each of EMF 2V and internal resistance 0.2 ohm are connected in series to an external resistor of 7.4 ohms. Calculate the current in the circuit.
3. A dry cell of EMF 1.6 V and internal resistance 0.1 ohm is connected to a resistor of resistance R ohms. If the current from the cell is 2 A, what is the p.d. across R? Determine the voltage drop across the resistance R₁ in the circuit given with E = 65 V. R₁ = 50 ohms, R₂ = 100 ohms, R₃ =100 ohms, R₄ = 300 ohms.

   

4. A battery of EMF 3V and internal resistance r is connected in series with a resistor of 55 ohms through an ammeter of resistance 1 ohm. Draw the circuit diagram and calculate the value of r if the ammeter reads 50 mA.
5. Two identical cells of EMF 1.5 V each joined in parallel to provide supply to an external circuit consisting of two resistances of 17 ohms each joined in parallel. A very high resistance voltmeter reads the terminal voltage of cells to be 1.4 V. Calculate the internal resistance of each cell.
6. In the circuit diagram given the cells E₁ and E₂ have EMF of 4 V and 8 V and internal resistance 0.5 ohm and 1 ohm respectively. Calculate the current in each resistance.

   

7. A set of n resistors, each of resistance R ohms, when connected in series have the effective resistance X and when connected in parallel have the effective resistance Y ohms. Find the relation between R, X, and Y.
8. A student obtains resistances of 3, 4, 12 and 16 ohms using only two metallic resistances wires either separately or joined together. What is the value of each of these wires?
9. A wire of uniform cross section and length l has a resistance of 16 ohms. It is cut into four equal parts. Each part is stretched to length l and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed. Assume that stretching of the wire does not cause any change in the density of its material.
10. Calculate the current drawn from the battery in the given network sketched here.

    

11. A voltmeter V of resistance 400 ohms is used to measure the potential difference across a 100 ohms resistor in the circuit shown here.
    (a) What will be the reading on thevoltmeter?
    (b) Calculate the potentiometer across 100 ohms resistor before the voltmeter is connected.

    

12. Calculate the resistance between A and B of the given network.

    

13. Three identical cells each of EMF 2 V and unknown internal resistance are connected in parallel. This combination is connected to a 5 ohms resistor. If the terminal voltage across the cells is 1.5 Volts, what is the internal resistance of each cell?
14. Calculate the current shown by the ammeter A in the circuit diagram given below.



15. Calculate the terminal voltage across The cell X and Y in the given circuit. The cell X has an emf of 4 V, internal Resistance 0.5 Ω and cell Y has an Emf of 8 V and internal resistance 1Ω.

    

16. Find the value of the unknown resistance X in the following circuit, if no current flows through the section AO. Also calculate the current drawn by the circuit from the battery of emf 6 V and negligible internal resistance.

    

17. Find the value of the unknown resistanc X in the following circuit, if no current flows through the section AO. Also calculate the current drawn by the circuit from the battery of emf 6 V and negligible internal resistance.

    

18. Four identical cells, each of emf 2 V, are joined in parallel providing supply of current to external circuit consisting of two 15Ω resistors joined in parallel. The terminal voltage of the cells as read by an ideal voltmeter is 1.6 V. Calculate the internal resistance of each cell.
19. Three identical cells each of emf 4 V and internal resistance ‘r’ are connected in series to a 6 Ω resistor. If the current flowing in the circuit is 1.5 A, calculate
    (I) the internal resistance of each cell and
    (ii) the terminal voltage across the cells.
20. in the given circuit diagram E₁ and E₂ are 2.0 V and 4.0 V respectively and B resistances r₁ and r₂ and R are 1.0 Ω, 2.0 Ω r₂ and 5.0 Ω respectively. Calculate the value of current and indicate its direction. Also calculate R the potential difference between the points
    (I) B and A and
    (ii) A and C.

    

21. In the given circuit, calculate the value of current in 4.5 Ω resistor and dicate the direction. Also calculate the potential Difference across each cell.

    

22. Six resistors, each of value 8 Ω are joined together in a circuit as shown in the figure. Calculate equivalent resistance across the points A and B. If a cell of emf 4 V is connected across AB, compute the current through the arms AB and DF of the circuit.

    

23. The V-I graphs of two resistors, and their series combination, are shown in the adjoining figure. Which of these graphs represent the series combination of the other two?Give reasons for your answer.

    

24. A voltmeter of resistance R_v and an ammeter of resistance R_A are connected in a circuit to measure, a resistance R as shown in the figure. The ratio of two meter readings gives an apparent resistance R’.Show that R and R’ are related by the relation
    !/R = 1/R’ – 1/R_v.

    

    1. A series combination of 2 K Ω resistor and a 1 K Ω resistor, is connected across a battery of emf 6 V and negligible internal resistance. The potential drop, across the 2 K Ω resistor is measured by
       (I) 30 K Ω
       (ii) a 1 K Ω voltmeter and
       (iii) both these voltmeters connected across it. If the voltmeter readings in the three cases are V₁, V₂ and V₃ respectively, arrange these reading in descending order.

How will the three readings compare with one another if the potential drop were measured across the series combination of 2 K Ω and 1 K Ω resistors.

26. Potential difference across terminals of a cell were measured (in volts) against different currents ( in ampere) flowing through the cell. A graph was drawn which has a straight line ABC.Using the data given in the graph determine,
    (I) the emf and
    (ii) the internal resistance of the cell.

    

27. Find the value of current in the circuit shown.

    

Submitted By Mr.Ashis kumar satapathy
Email Id :[email protected]