CBSE Guess > Papers > Important Questions > Class XII > Physics > Physics (Current & electricity) By: Mr. Abhishek Gupta

Current & Electricity

Q. 1. Give an example of a superconductor

Q. 2. What is current? Mention its SI unit.

Q. 3. Name 2 materials, which are used for making standard resistance coils.

Q. 4. What is the resistance corresponding to Red, Blue, Yellow and Silver?

Q. 5. Mention the colour coding for a 250-ohm resistor

Q. 6. How can a potentiometer be made more sensitive?

Q. 7. Name 2 defects of the voltaic cell. How are they removed?

Q. 8. When 2 resistors are joined in series, the net is 9 ohm. When these 2 resistors are joined in parallel the net is 2 ohm. Find the value of these resistors.

Q. 9. What are the possible values of resistances that can be obtained using 5ohm and 10ohm.

Q. 10. A set of n identical resistors each of resistance R, when connected in series give a net of X ohm and when connected in parallel give a net of Y ohm. Show that XY=R²

Q. 11. In a current carrying wire, 6 x 10²³ electrons flow in 5 seconds. Find the current

Q. 12. A series combination of 2-ohm and 1-ohm resistors is connected across a battery of 6V and negligible internal resistance. The potential difference across the 2 ohm resistor is found using a

1. 30K-ohm voltmeter
2. 1K ohm voltmeter
3. Potentiometer

If the readings obtained are V1, V2 and V3 then arrange them is ascending order.

Q. 13. Write a note on superconductivity explaining its cause and application. What is critical temperature.

Q. 14. State and derive ohm’s law. What is resistivity ?

Q. 15. A resistance has color coding as ( green,Red,brown,) and other one has (blue,black,grey).

Find the ratio of power dissipated in first to the power dissipated in second if both are separately connected across 220V-power supply.

Q. 16. Using proper figure, explain why a voltmeter is connected in parallel but ammeter in series.

Q. 17. What is the cause of resistance. On what factors does it depend.

Q. 18. Three resistors 8Ω , 4Ω and 6Ω are connected in parallel across a cell. The net current drawn from the cell is I₁. When they are joined in series across the same cell the net current drawn is I₂.

Find the ratio I₁ / I₂ . Also determine the current through each resistance separately in both the cases.

Q. 19. A silver wire has a resistance of 2.0 ohms at 20^oC and a resistance of 2.5 ohms at 100oC. Determine the temp coeff of resistance.

Q. 20. The maximum power rating of a 20-ohm resistor is 2.0KW ( That is, this is the maximum power the resistor can dissipate without melting ) Would you connect this resistor directly across a 300V DC supply. Explain. Can we connect two such resistors in series across the 300V supply?

Q. 21. In a meter bridge experiment, a fixed resistance of 10ohms is used. The balance length obtained while finding an unknown resistance is 40cm. Find the unknown resistance.

Q. 22. Give reasons

1. The electron drift speed is estimated to be only a few mm/s . How can such a small speed account for instantaneous current
2. Is a wire carrying current charged ? Why or why not

Q. 23. An electric bulb is marked as 100W at 200V. Find the power dissipated if instead of 200V supply the bulb is joined to

1. 400 volt supply
2. 2A constant current source

Q. 24. A wire of uniform cross section and length L has a resistance of 16ohm. It is cut into four equal parts. Each part is stretched uniformly to length L and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed.

Q. 25. A galvanometer has a coil resistance of 5-ohm and a current rating of 500mA. Explain how this can be converted into a

1. Voltmeter of range 10 volts
2. Ammeter of range 5A

In each case, find the net resistance of the device

Q. 26. A house is fitted with 10 bulbs of 50W-200V each, 8 fans consuming 0.5 ampere at 200V each and an electric iron having a resistance of 250 ohms. If the power supplied is at 200Volts and the cost of energy is Rs. 5 per kWh. find the electricity bill for the month of June if all the above appliances are used for 5 hours in a day.

Q. 27. In a thermocouple the Emf varies with temp as E = AT - BT². Where T is the temp of the hot junction and the cold junction is kept at 0^oC. Here Emf is in μV and T is in ^oC. The value of

A is 4 μV^oC^-1 and B is 0.04 μV^oC^-2 where μ = 10^-6. Find

1. Neutral temp.
2. inversion temp
3. emf at 120^oC
4. thermoelectric power at 120^oC
5. thermoelectric power at neutral temp