Power wasted/delivered to a resistor

In summary, two 8 ohm resistors and a battery of emf 12.0V and internal resistance of 8ohms are connected in series. Calculate the power delivered to each external resistor and then calculate the power wasted due to internal resistance. I keep coming up with the answer 18 but apparently that is not right, and I am strugglying, so help would be much appreciated.
  • #1
chris858
Gold Member
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Homework Statement


two 8 ohm resistors and a battery of emf 12.0V and internal resistance of 8ohms are connected in series. Calculate the power delivered to each external resistor and then calculate the power wasted due to internal resistance.
I keep coming up with the answer 18 but apparently that is not right, and I am strugglying, so help would be much appreciated.

Homework Equations


W=IV
I=V/R

The Attempt at a Solution


VxV/R
12 X 12/8 =18...
current = 1.5A
 
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  • #2
chris858 said:

Homework Statement


two 8 ohm resistors and a battery of emf 12.0V and internal resistance of 8ohms are connected in series. Calculate the power delivered to each external resistor and then calculate the power wasted due to internal resistance.
I keep coming up with the answer 18 but apparently that is not right, and I am strugglying, so help would be much appreciated.

Homework Equations


W=IV
I=V/R

The Attempt at a Solution


VxV/R
12 X 12/8 =18...
current = 1.5A
Sketch the circuit. How many resistors does the current flow through? What's the total resistance that the current flows through? So what then the current?
 
  • #3
flows through two resistors, total resistance = 16 ohms. Current = 12/16 =0.75A
 
  • #4
chris858 said:
flows through two resistors, total resistance = 16 ohms. Current = 12/16 =0.75A
What about the battery's internal resistance?
 
  • #5
16+8=24 so 12/24=0.5A
 
  • #6
chris858 said:
16+8=24 so 12/24=0.5A
Right. So now what will you do now that you know the current through each resistor?
 
  • #7
pwer= voltage times voltage over current. p=VxV/R so 12x 12/0.5=2
 
  • #8
chris858 said:
pwer= voltage times voltage over current. p=VxV/R so 12x 12/0.5=2
R is not current in the formula P = V2/R, it represents resistance.

There are other formulas for power. What are they?

Oh, and be sure to include units with all results.
 
  • #9
power = work/time
P=IV
P=V²/R
P=RI²
 
  • #10
power is measured in watts
current in amps
resistance in ohms
voltage in volts
 
  • #11
Okay, so what is the power dissipated by one of the resistors?
 
  • #12
I get it now, so basically the equation i was using gave the total power watts, which is actually 6 not 2, and so there are 3 resistors, including the internal resistance, so therefore you have to divide 6 by 3 which gives 2.0Watts per resistor.
Thankyou very much!
 

FAQ: Power wasted/delivered to a resistor

1. What is power wasted/delivered to a resistor?

Power wasted/delivered to a resistor refers to the amount of energy that is either converted into heat or used by a resistor in an electrical circuit. It is measured in watts (W) and is calculated by multiplying the current (I) through the resistor by the voltage (V) across the resistor.

2. Why is power wasted/delivered to a resistor important?

Power wasted/delivered to a resistor is important because it helps determine the efficiency of an electrical circuit. It also helps in selecting the appropriate resistor for a circuit to ensure it can handle the power being delivered to it without overheating.

3. How does the resistance of a resistor affect power wasted/delivered?

The resistance of a resistor directly affects the power wasted/delivered to it. As the resistance increases, the amount of power wasted/delivered also increases. This is because a higher resistance means a larger voltage drop across the resistor, resulting in more power being dissipated as heat.

4. Can power wasted/delivered to a resistor be controlled?

Yes, power wasted/delivered to a resistor can be controlled by adjusting the current or voltage in the circuit. By decreasing the current or voltage, the power wasted/delivered to a resistor can be reduced, thus increasing the overall efficiency of the circuit.

5. What happens if too much power is wasted/delivered to a resistor?

If too much power is wasted/delivered to a resistor, it can lead to overheating and potentially damaging the resistor. This can cause the resistor to fail and result in the circuit not functioning properly. It is important to select a resistor with the appropriate power rating to prevent this from happening.

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