Current in the curcuit from watts and volts

In summary, the circuit has a 50 V battery and three resistors with a total power of 75 watts. The attempt at a solution involved finding the equalizing resistance and using V=IR to calculate the current, but the student was unsure of how to incorporate watts into the equation. The solution was to work out the resistors individually using P=I*I*R and then using the fact that the two resistors in parallel have the same resistance.
  • #1
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Homework Statement



A circuit has a 50 V battery, and 3 resistors. they are all 25 Watts, 1 is in series, 2 are parallel. Find the current of the circuit.

Homework Equations



V=IR
P=IV

The Attempt at a Solution



I know how to do these fine when I'm given the resistances or the amperages, but I'm having problems with this style.

I've attempted this a few different ways. I tried to find the equalizing resistance using: P=v^2/R
25=50^2/R
R=100 ohms.

then 1/100 + 1/100 = 1/Rparallel = 50. 50+100=150. to find the equalizing resistance, and then using:
V=IR
120=I*150
I= .8 Amps.

I'm clearly missing something when I'm working with Watts... can someone please walk me through how to actually do this. it's very urgent...
 
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  • #2
The 3 resistors together use 25 + 25 + 25 = 75 watts.

This must come from the battery, so how much current is being drawn?

After that it is easy.

Work out each resistor knowing the power in it and the current (P=I*I*R). The two in parallel have the same resistance but you need to see why this has to be the case.
 
  • #3
thanks
 
  • #4
Actually, the question doesn't ask for the size of the resistors or the voltage across them. But it would be excellent practice for you to work them out.
They come out easily.
 

FAQ: Current in the curcuit from watts and volts

What is the difference between watts and volts?

Watts and volts are both units used to measure electricity. Watts measure the rate of energy transfer, while volts measure the amount of force pushing the electricity through a circuit. In simpler terms, watts measure how much work can be done by the electricity, while volts measure the intensity of the electricity.

How are watts and volts related in a circuit?

Watts and volts are related through the equation P = VI, where P is power in watts, V is voltage in volts, and I is current in amperes. This means that power is equal to voltage multiplied by current. In other words, watts are dependent on both volts and the amount of current flowing through the circuit.

How does current affect the flow of electricity in a circuit?

Current is the measure of the flow of electricity in a circuit. It is directly proportional to the amount of voltage applied and inversely proportional to the resistance of the circuit. This means that as the current increases, the flow of electricity also increases, but as the resistance increases, the flow of electricity decreases.

What happens to the current in a circuit if the voltage is doubled?

If the voltage in a circuit is doubled, the current will also double, assuming the resistance remains the same. This is because of the relationship between voltage and current described by Ohm's Law, which states that current is directly proportional to voltage.

How do watts and volts affect the efficiency of a circuit?

Watts and volts do not directly affect the efficiency of a circuit. However, they do play a role in determining the power of the circuit, which can affect efficiency. In general, a higher voltage can lead to a more efficient circuit, as it allows for more work to be done with less current and therefore less waste of energy.

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