Name.docx

Name_______________________________________________ Roll Number__________________________________________ Instructions: (1) Detailed calculations must be shown (2) Answers must be written within the space provided. You can use pencil if you need to erase Question 1

True or False: To get Galvanometer NULL (zero current in the Galvanometer) the circuit must satisfy

Question 2 Connect a guard-wire to bypass the surface current in the following diagram [1]

𝑃 𝑅

=

𝐴 𝐵

[1]

Question 3 We have an ammeter with full scale deflection current = 1 mA and internal resistance of 700 Ω. (a) Convert this ammeter into a multi-range voltmeter with ranges as (i) 0-1 V and (ii) 0-10 V. Draw the circuit diagram and label all the circuit elements with their values. [3]

(b) When your (above) voltmeter is used to measure an unknown voltage in the 0-10 V range, the meter is found to indicate 0.6mA. What is the value of the unknown voltage? [1]

Question 4 Show with a very clear diagram how a 4-terminal shunt is to be connected to an ammeter to change the range. (The 4 terminals must be clearly marked. Also the current inlet and outlet (i.e. where we should connect external circuits) of the measuring circuit must be clearly marked.) [3]

Question 5 An unknown resistance Rx is to be measured using a voltmeter (with internal resistance 1100Ω) and an ammeter (with internal resistance 10 Ω). (a) Draw the circuit diagram of your choice. (b) In your circuit the voltmeter reading is found to be 10V and the ammeter reading is found to be 0.1A. Find the true value of Rx. [6]

Note: In the laboratory we do not estimate true resistance in this way because we generally do not know the internal resistance of a voltmeter or an ammeter.

Question 6 Answer one of the following questions (the questions have different marks according to the level of difficulty). Clearly write which question you are choosing (a) Insert in the following circuit a compensated wattmeter such that the wattmeter reading always indicates the power supplied by the source and label all the coils and show the electrical connections/junctions between the coils very clearly. [6] (b) Insert in the following circuit a compensated wattmeter such that the wattmeter reading always indicates the power consumed by the load and label all the coils and show the electrical connections/junctions between the coils very clearly. [5] (c) Insert in the following circuit an uncompensated wattmeter that approximately indicates the source or the load power [3]

Question 7 We want to measure an voltage which lies between 8KV to 10KV. We have a voltmeter (with internal resistance of 1KΩ) that can measure up to 10V. (a) Range changing scheme 1: Use suitable series resistance to change the range of the voltmeter to an appropriate value. How much will be the internal resistance of the new voltmeter circuit? [2]

(b) Range changing scheme 1: We have a 1000:1 transformer (assume to be ideal). Show how this transformer can be used together with the 10V voltmeter to measure the unknown voltage. How much will be the internal resistance of the measuring system? [3]

(c) Which scheme is preferable from the point of internal resistance OR power consumption? [1]

Question 8 We have a variable standard mutual inductor. Using this, we have to measure an unknown mutual inductance. Show how to do this with circuit diagram and equations. [3]

1. A PMMC instrument has air gap flux density of 0.5 Tesla, coil dimension of 2cm×2cm, number of turns = 200. Spring constant = 1 micro Nm/degree. If 1 mA current flows through the coil, how much deflection will be produced? [3] 2. How much shunt resistance is to be connected to a 10mA ammeter to change its range to 1A. The coil resistance is 99 Ω [2] 3. (a) Draw a schematic potentiometer circuit with provision to switch between the standard cell and the unknown cell. (b) Let the length of the potentiometer wire is 1m, the resistance of the potentiometer wire is 2Ω, the current flowing through the potentiometer wire is 1A. While measuring an unknown voltage source, the balance is obtained at 75 cm. What is the value of the unknown source? (c) If the least count of the potentiometer scale is 1mm, then what is the precision/resolution of this measurement? [3] 4. Draw a clear circuit diagram showing how a wattmeter is to be connected to measure power [3] 5. Find the balance equation of the following bridge [3]

6. Define Q factor of an Inductor

[1]