An electric lamp with resistance Rd and an ammeter were connected to a 200 V network as shown in Figure
| August 5, 2021 | education
An electric lamp with resistance Rd and an ammeter were connected to a 200 V network as shown in Figure 165. Calculate the resistance Rd if the ammeter shows a current of 0.5 A. The resistance of the lamp is 240 ohms.
Ohm’s law says: the current is directly proportional to the applied voltage and inversely proportional to the resistance of the circuit or I = U / R, where R is the total resistance of the circuit, in this case it is equal to: Rl + Rd. We neglect the resistance of the ammeter since it is small, then
we get:
0.5 = 200 / (240 + Rd)
240 + Rd = 200 / 0.5 = 400
Rd = 400-240 = 160 Ohm
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