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
- 30K-ohm voltmeter
- 1K ohm voltmeter
- 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 20oC 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
- The electron drift speed is estimated to be only a few mm/s . How can such a small speed account for instantaneous current
- 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
- 400 volt supply
- 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
- Voltmeter of range 10 volts
- 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 0oC. Here Emf is in μV and T is in oC. The value of
A is 4 μVoC-1 and B is 0.04 μVoC-2 where μ = 10-6. Find
- Neutral temp.
- inversion temp
- emf at 120oC
- thermoelectric power at 120oC
- thermoelectric power at neutral temp
| Physics Links | |
| 1. | Atomic Nucleus |
| 2. | Current & Electricity 1 |
| 3. | Current & Electricity 2 |
| 4. | Electrostatics 1 |
| 5. | Electrostatics 2 |
| 6. | Magnetism 1 |
| 7. | Magnetism And Magnetic Effect Of Current 2 |
| 8. | Optics 1 |
| 9. | EMI, AC And Optics |
| 10. | Magnetism And Magnetic Effect Of Current |
| 11. | Optics 2 |
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