*** SOME IMPORTANT SHORT QUESTIONS OF PHYSICS 12 FOR BOARD EAXM 2071 *** Short Questions - Answer #Electrical__Circuit #Grade: XII 1. “Wheatstone Bridge method of determination of resistance is considered to be more accurate than the voltmeter-ammeter method.” Why? Ans. Wheatstone bridge method is a null deflection method. The resistance determined does not depend on the deflection of the galvanometer and the supply voltage fluctuations. So, it is more accurate than other methods. 2. “Wheatstone Bridge in not suitable for measuring high resistance.” Why? Ans. While measuring a low resistance, all the other resistances must also be low so that the bridge is sensitive. A low resistance galvanometer is insensitive. Further, the load resistance and contact resistance will also introduce error in the measurement. 3. What is meant by end correction for the meter bridge? Ans. The two ends of the wire not exactly coincide with the zero mark and 100 cm mark of the meter scale. Also the two ends of the one meter wire need not be in good contact with the copper stripes at the ends. A correction has to be applied for this. This is called end correction. 4. Why do we prefer potentiometer of longer length for accurate measurement? Ans. The longer is the length of the potentiometer wire, the higher is the accuracy because the potential drop on the wire per unit length decreases as the length of the wire increases. Hence, the potentiometer measures emf more accurately. 5. What do you mean by potential gradient of a potentiometer? Ans. The potentiometer difference per unit length of the wire of a potentiometer is called its potential gradient. Smaller the potential gradient betters its sensitivity. 6. “Kirchhoff’s is law preferred over Ohms’ law” why? Ans. When an electrical circuit contains many sources of emf, the circuit may be analyzed easily using Kirchhoff’s law. 7. “Kirchhoff’s laws are related to a certain conservation laws” Name them. Ans. Kirchhoff’s first law is based on the law of conservation of charge and the second law based on the law of conservation of energy. 8. Why is a meter bridge so named? Ans. Since the length of wire fixed on the board is one meter and instrument is based on the circuit of Wheatstone bridge. Hence the instrument is named as meter-bridge. 9. Why should the cross section of potentiometer wire be uniformed? Ans. If the cross section of potentiometer wire is not uniform, then potential gradient will not be same at all place on the potentiometer wire. Consequently, the measured value of potential difference will not be correct. 10. Why is post office box so named? Ans. The instrument was designed to measure the resistance of telegraph wire in a post office. That is why it is known as post office box.
Posted on: Thu, 13 Mar 2014 15:21:53 +0000
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