Question about changing resistance and power

In summary, the conversation discusses the difference in resistance of a 60W filament lamp when connected to a 6.0 V battery compared to a 230V supply. The student's explanation involves the relationship between voltage, resistance, and power, while the answer scheme mentions the effect of temperature on resistance. The student questions the validity of their explanation, but the answer scheme does not address this.
  • #1
MBBphys
Gold Member
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Homework Statement


So this was the question:
The 60W filament lamp is connected to a 6.0 V battery. The resistance of the lamp in this circuit is 70 Ohms. Explain why this value differs from the value given in (a)(iv) when the lamp is connected to the 230V supply.

My answer was:
V=IR, P=IV, I=V/R
Therefore,
P=(V^2)/R
P is a constant here (60W)
Hence, (V^2) is directly proportional to R, so as we connect the lamp to a lower voltage battery, we measure a lower resistance.

However, the answer scheme said this:

The resistance of a metal increases with temperature. At 6V, lower heating effect, hence lower resistance.

So is there anything wrong with the argument I gave?

Thank you very much in advance!

Homework Equations


V=IR
P=IV

The Attempt at a Solution


(Shown above)
 
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  • #2
MBBphys said:
The 60W filament lamp is connected to a 6.0 V battery. The resistance of the lamp in this circuit is 70 Ohms.
So the power dissipated by the bulb here is obviously not 60W, right? The bulb is probably not glowing when connected to only a 6V source...
MBBphys said:
differs from the value given in (a)(iv)
What's (a)(iv)? Is there a figure that goes with this question?
 

1. What is resistance and how does it affect power?

Resistance is a measure of how difficult it is for electric current to flow through a material. It is measured in ohms (Ω). The higher the resistance, the more difficult it is for current to flow through the material, resulting in less power being delivered to a circuit.

2. Can resistance be changed?

Yes, resistance can be changed by altering the properties of the material or by adding components such as resistors to a circuit. For example, materials with higher resistivity will have a higher resistance, while materials with lower resistivity will have a lower resistance.

3. How does changing resistance affect the power in a circuit?

Changing the resistance in a circuit can affect the power by either increasing or decreasing it. When resistance is increased, the power decreases, as it becomes more difficult for current to flow through the circuit. Conversely, decreasing resistance can result in an increase in power.

4. What is the relationship between resistance and power in a circuit?

The relationship between resistance and power in a circuit is described by Ohm's law, which states that power is equal to the square of the current multiplied by the resistance (P = I^2R). This means that as resistance increases, power decreases, and vice versa.

5. Can changing resistance affect the efficiency of a circuit?

Yes, changing resistance can affect the efficiency of a circuit. Higher resistance can result in a decrease in efficiency, as more energy is lost as heat. However, in some cases, adding resistance can improve efficiency by regulating the flow of current and preventing damage to components.

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