Determining voltage across resistor and current direction

In summary, a resistor with a resistance of 8 ohms is connected to an unknown network N and is immersed in an isolated water bath. The power dissipated in the resistor is 11 W. Part a) of the problem asks to find the voltage across the resistor, which has been ignored. For part b), the current entering the network N from the resistor is determined to be -1.17A due to the passive nature of the resistor. This negative sign is necessary to maintain mathematical accuracy in the calculation of power, which is I2.R.
  • #1
LongApple
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Homework Statement



Resistor conected to unknown network N. Resistor immersed in isolated water bath. Resistor resistance R = 8 ohms. It is determined the power dissipated in resistor is 11 W

a) Find the voltage across the resistor.

b) What is the current i entering the network N from the resistor?
[/B]
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Homework Equations



V=IR

The Attempt at a Solution



Ignore part a). I understand my mistake for that one.

For part b) though I am trying to get a better intuition for what in this problem would tell us that current is actually leaving the network as opposed to entering it. What is the physical intuition for why that is the case and what is the matematical reason part b) has a negative -1.17 A?
 
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  • #2
The resistor is a passive element, it does not source current. So we know the current through the resistor is coming out of the network, and it's 1.17A.

So, 1.17A out of the network can be expressed as negative current INTO the network. The question asks for the current entering the network from the resistor, this must therefore be negative 1.17A, i.e., -1.17A. It's just the way it's done to stay mathematically correct at all times.

Power is I2.R so any negative sign disappears in the power calculation.
 

Related to Determining voltage across resistor and current direction

1. How do you determine the voltage across a resistor?

The voltage across a resistor can be determined by using Ohm's Law, which states that the voltage (V) is equal to the current (I) multiplied by the resistance (R). This can be expressed as V = I * R. Alternatively, you can use a voltmeter to directly measure the voltage across the resistor.

2. What is the relationship between voltage and current in a resistor?

In a resistor, the voltage and current are directly proportional to each other. This means that as the voltage increases, the current will also increase, and vice versa. This relationship is described by Ohm's Law, where the resistance (R) of the resistor remains constant.

3. How do you determine the direction of current in a circuit?

The direction of current flow in a circuit can be determined by using the right-hand rule. This rule states that if you point your thumb in the direction of the current, then your fingers will wrap around in the direction of the magnetic field. You can also use a multimeter to measure the direction of current flow.

4. What is the purpose of determining the voltage across a resistor?

Determining the voltage across a resistor is important for understanding the behavior of a circuit and calculating the power dissipated by the resistor. It can also help in troubleshooting and identifying any issues with the circuit.

5. How do you calculate the power dissipated by a resistor?

The power dissipated by a resistor can be calculated using the formula P = V * I, where P is power in watts, V is voltage in volts, and I is current in amperes. This formula can also be expressed as P = I^2 * R, or P = V^2 / R, depending on the information you have available.

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