Questions and exercises Am 0.05 ade 1. A student tried to test a lab-made Ammeter with a DMM using the circuit in Fig. 6. When the output voltage of the DC power supply was adjusted to 5V the fuse in DMM was blown. DC power supply Switch A1 DMM Potentiometer R = 100 2 Ammeter A2 (lab-made) Figure 6 A circuit made by a student to test lab-made Ammeter with a DMM (a) Explain why the circuit in Fig. 6 can cause the fuse in DMM to blown. (b) Draw a correct circuit for testing a lab-made Ammeter with a DMM. (c) Suppose you have a galvanometer with a full-scale current Ic = 50 A and an internal resistance r = 200 2. What resistance value of a shunt resistor should be used for making a dc ammeter with a maximum scale reading Imax = 150 mA? 2. A student tried to test a lab-made Voltmeter with a DMM using the circuit in Fig. 7. When the output voltage of the DC power supply was slowly increased, the voltage reading on DMM follows the output voltage of the power supply, however, the voltage reading on the lab-made voltmeter is always zero. No damage to any part in the circuit was found. Potentiometer Switch R = 50 KQ V1 DMM DC power supply V2 Voltmeter (lab-made) Figure 7 A circuit made by a student to test lab-made Voltmeter with a DMM 37 (a) Since no damage to any part in the circuit was found, explain why the circuit in Fig. 7 does not affect the voltage reading on DMM, however, it does make zero voltage reading on the lab-made voltmeter. (b) Draw a correct circuit for testing a lab-made Voltmeter with a DMM. MMG 43 nog (c) Suppose you have a galvanometer with a full-scale current Ic = 50 A and an internal resistance m-dr = 200 2. What resistance value of a multiplier resistor should be used for making a dc voltmeter with a maximum scale reading Vmax = 20 V? -