Key relationship
Econductor=0 inside; Euniform-insulator∝r inside; Eoutside∝1/r².
Physics · Class 12
Free charge in conductors and insulators
Free charges redistribute in an electrostatic conductor until the interior field vanishes. A fixed uniform charge density in an insulating sphere instead gives an interior field proportional to radius.
Open the interactive experiment →Free charge in conductors and insulators
கடத்தியில் சுதந்திர மின்னூட்டங்கள் நகர்ந்து உள்ள்புலத்தை பூஜ்யமாக்கும். மின்காப்பானில் மின்னூட்டம் நிலையாக இருக்கலாம்.
Key notes, relationships and model limits
Remember
Free charges redistribute in an electrostatic conductor until the interior field vanishes. A fixed uniform charge density in an insulating sphere instead gives an interior field proportional to radius.
Common trap
A conductor has zero interior electric field in electrostatic equilibrium, while an insulating charged sphere can have a nonzero interior field.
Model limits
Spherical symmetry, electrostatic equilibrium for conductor, uniform immobile volume charge for insulator. Surface density readout describes conductor only.
What you will learn
Use the controls and plotted relation to explain free charge in conductors and insulators.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
A sphere with surface E=1000 N/C has conductor interior E=0; a uniform insulator at half-radius has E=500 N/C.
Why this matters
The model connects free charge in conductors and insulators with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
What is E inside an electrostatic conductor?
- A uniform nonzero field set by the conductor size.
- Zero after free charges reach equilibrium.
- A field proportional to distance from the centre.
Read the explanation
Zero after free charges reach equilibrium.
Course connection: Class XII Chapter 2. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.