CBSE Class 12 Physics Current Electricity Formulae

1. What happens to the power dissipation if the value of electric current passing through a conductor of constant resistance is doubled.

2 external resistance. What will be the current in circuit? W is connected to a 3.9 W2. A cell of emf 2 V and internal résistance 0.1

3. Calculate the resistivity of a material of a wire 1 m long, 0.4 mm in diameter and having a resistance of 2 ohm.

4. 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?

5. A current is maintained in a conductor of cross-section 10-4 m2. If the number density of free electrons be 9 x 1028 m-3and the drift velocity of free electrons be 6.94 x10 – 9 m/s, calculate the current in the conductor.

6. A silver wire has a resistance of 2.1 Ω at 27.5 ⁰C, and a resistance of 2.7 Ω at 100 ⁰C. Determine the temperature coefficient of resistivity of silver.

7. Three resistors 1 Ω, 2 Ω and 3 Ω are combined in series. (a) 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, determine the total current drawn from the battery.

8. (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 and the total current drawn from the battery.

9. A Voltage of 30V is applied across a carbon resistor with first second and third rings of blue, black and yellow colours respectively. Calculate the value of current in mA, through the resistor.

10. In a meter bridge the balance point is found to be 39.5 cm from one end A, when the resistor Y is of 12.5Ω . Determine the resistance of X.

WORKSHEET (NUMERICALS) : LEVEL - II
1. A cell of emf 2 V and internal résistance 0.1 Ω is connected to a 3.9 Ω external resistance. What will be the p.d. across the terminals of the cell?

2. Out of the two bulbs marked 25W and 100W, which one has higher resistance.

3. A cell of 6 V and internal resistance 2Ω is connected to a variable resistor. For what value of current does maximum power dissipation occur in the circuit?

4. What is the largest voltage you can safely put across a resistor marked 98 Ω - 0.5 W?

5. Two heater wires of the same dimensions are first connected in series and them in parallel to a source of supply . What will be ratio of heat produced in two cases?

6. Using data given in graph determine (i) emf (ii) internal resistance of the cell.
(iii) For what current, does maximum power dissipation occur in the circuit?

7. You are given ‘n’ resistors each of resistance ‘r’. These are first connected to get of minimum possible resistance. In the second case these are again connected differently to get maximum possible resistance. Compute the ratio between the maximum and minimum values resistance so obtained.

8.Two primary cells of emf E1 and E2 (E1 > E2) are connected to the potentiometer wire as shown in the figure. If the balancing lengths for the cells are 250 cm and 400 cm. Find the ratio of E1 and E2.

9. Two identical cells of emf 1.5V each are joined in parallel providing supply to an external circuit consisting of two resistors of 13 each joined in parallel. A very high resistance voltmeter reads the terminal voltage of the cells to be 1.4V. Find the internal resistance of each cell.

10. Three cells of emf 2V, 1.8V and 1.5V are connected in series. Their internal resistances are 0.05Ω, 0.7Ω and 1Ω respectively. If this battery is connected to an external resistance of 4Ω, calculate :
(i) the total current flowing in the circuit. (ii) the p.d. across the terminals of the cell of emf 1.5V.

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