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# Basic electrical circuit engineering

A circuit consists of three resistors in series, with values 200 ohms, 100 ohms and 60 ohms. The circuit is connected to a battery with an output of 36 volts.

a. What is the current flowing in the series circuit?

b. The battery is replaced by a sine wave source with a frequency of 60.0 Hz and a peak voltage 36.0 volts. What is the RMS current flowing in the series circuit?

c. In the circuit described in part (b) above, how much power is dissipated in the 200 ohms resistor?

d. A telephone handset has a resistance of 600 ohms. It is connected to the local telephone exchange at a distance of 5 km by a twisted pair that has a loop resistance of 200 ohms per km. The telephone exchange has a 48.0 V battery that is connected to the twisted pair through a 400 ohms resistor. What is the DC current through the handset when it is off-hook?

#### Solution Preview

Please see the attachment as well for clear symbols and drawing in (d).

(a) As it is a series circuit with just resistance we can say that by Ohm's law

Voltage (V) = Current (I) x Total Resistance (R (tot))

i.e. V = IR(tot) (1)

We are asked to find the current so we rearrange (1) to make I the subject when we do this we get (2).

I = V/R(tot) (2)

Now total resistance is sum of series resistance so we can deduce

R(tot) = 100 + 200 + 60 Ohms = 360 Ohms

Now we ...

#### Solution Summary

A series circuit is examined with three given series pure resistances. A battery is connected of known DC voltage and the current flowing in the series circuit deduced. A sine wave generator of know amplitude and frequency replaces the battery and the RMS current that flows and the power dissipated is deduced. A telephone line of known parameters is given and the DC current that flows through the handset for such a system is deduced.

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