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1.) Suppose switches S1 and S2 are BOTH closed (allowing for current to flow thr

ID: 2278972 • Letter: 1

Question


1.) Suppose switches S1 and S2 are BOTH closed (allowing for current to flow through) and the other switches are open. Determine the total current and power supplied by the voltage supply. What is the power dissipated in each resister? Do both the bulb and the hairdryer operate normally?


4.) Suppose switches S1 and S2 are closed as in the previous part. Also suppose your cat chews on the power cord the wires in the cord touch, the effect is the same as closing switch S4 so that 1 ? short-circuit resistance becomes part of the circuit. (The cat is quick and gets away safely.) Determine the current and power supplied by the voltage supply. Where in the circuit is almost all of the power dissapated?

Note that the wattage value listed on the bulb package assumes that 120 volts will be applied across the bulb. If a different voltage is applied to the bulb (or hairdryer), a different amount of power will be used. Regardless of the voltage applied, the resistance of each remains constant. So, we can think of each appliance as a resistor sitting in the circuit. Switches S1, S2, S3, and S4 can be open (no current will flow) or closed (current flows through the switch freely). Resistors R1 and R3 are the 60 W bulbs, R2 is the 1500 W hairdryer and R4 is the 100 W light bulb. Switch S4 is open for now. The resistor r is 1 ohm. It represents a possible short-circuit that develops if switch S4 is dosed.

Explanation / Answer

1.) S1 and S2 are closed


total current = i1 + i2


i1 = current through 60W bulb

i2 = curreny through 1500 W hairdryer


=> total current = i = 60/120 + 1500/120 = 13 Amps


total power = total currec*voltage = 13*120 = 1560 W


power dissipated in each is 60 W and 1500 W and both function normally


4.) if S4 is closed and the circuit is short because of r = 1 ohm


no current would flow through r1,r2 and r3


and total current = 120/1 =120 Amps


total power = I*V = 120^2 = 14400 W


total power is dissipated at r = 1 ohm resistor