What Voltage Is Required to Melt Lead with a Capacitor?

  • Thread starter Thread starter Touchme
  • Start date Start date
  • Tags Tags
    Capacitor
Click For Summary
SUMMARY

The discussion focuses on calculating the voltage required to melt a 7.00 mg sample of lead using a 55.0 µF capacitor. The energy needed to raise the temperature of the lead to its melting point and then melt it is calculated using the formulas Q = mCT and Q = mL. The user initially calculated the required energy as 446.84 J and derived a voltage of 4030.97 V. However, the error identified was in the mass conversion, where 7 mg was incorrectly treated as 7 g, necessitating a correction in the calculations.

PREREQUISITES
  • Understanding of capacitor energy storage (Energy stored = (1/2)C(V)^2)
  • Knowledge of specific heat and latent heat concepts (Q = mCT and Q = mL)
  • Ability to convert units accurately (milligrams to kilograms)
  • Familiarity with thermal energy calculations
NEXT STEPS
  • Review the principles of energy storage in capacitors, focusing on the formula Energy stored = (1/2)C(V)^2.
  • Study the concepts of specific heat and latent heat, particularly in the context of phase changes.
  • Practice unit conversion techniques, especially for mass in thermal energy calculations.
  • Explore examples of thermal energy calculations involving different materials and their properties.
USEFUL FOR

Students in physics or engineering, particularly those studying thermodynamics and electrical energy storage, as well as anyone involved in practical applications of capacitors in heating processes.

Touchme
Messages
41
Reaction score
0

Homework Statement



The energy stored in a 55.0 µF capacitor is used to melt a 7.00 mg sample of lead. To what voltage must the capacitor be initially charged, assuming that the initial temperature of the lead is 20.0°C? Lead has a specific heat of 128 J/kg°C, a melting point of 327.3°C, and a latent heat of fusion of 24.5 kJ/kg.


Homework Equations



Energy stored = (1/2)C(V)^2
Q=mCT
Q=mL

The Attempt at a Solution



Basically I found the heat energy require to melt the lead.
Q = mCT + mL = (0.007)(128)(327.3-20.0) + (0.007)(24500)
Q = 446.84 J

Then I used energy stored = (1/2)C(V)^2
446.84 = (1/2)(55e-6)(V)^2
sq.root(893.68/(55e-6)) = V

V = 4030.97 V

What am I doing wrong?Help
 
Last edited:
Physics news on Phys.org
I think you've just become confused with units. The question states 7 milligrams of lead and you have used 7 grams in your calculations. Since your latent heat and specific heat are given to be used with kilograms you have to be careful.
 
Last edited:

Similar threads

  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
8
Views
2K
  • · Replies 6 ·
Replies
6
Views
4K
Replies
5
Views
2K
  • · Replies 13 ·
Replies
13
Views
4K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 28 ·
Replies
28
Views
3K
Replies
3
Views
7K