Question

What is called susceptibility?

Answer 1

Susceptibility is a measure of how much a material gets influenced by an external field. It is commonly used in **electromagnetism** and **materials science** to describe how a material responds to applied electric or magnetic fields.

### **Types of Susceptibility:**
1. **Electric Susceptibility (\(\chi_e\))**  
   - It measures how easily a material gets **polarized** when an external **electric field** is applied.  
   - It is related to the **permittivity** of the material:  
     \[
     \varepsilon = \varepsilon_0 (1 + \chi_e)
     \]
   - Where \( \varepsilon \) is the material's permittivity, \( \varepsilon_0 \) is the permittivity of free space, and \( \chi_e \) is the electric susceptibility.

2. **Magnetic Susceptibility (\(\chi_m\))**  
   - It measures how much a material gets **magnetized** when placed in an external **magnetic field**.  
   - It is given by:  
     \[
     M = \chi_m H
     \]
   - Where \( M \) is the magnetization, \( H \) is the applied magnetic field, and \( \chi_m \) is the magnetic susceptibility.
   - If \( \chi_m > 0 \), the material is **paramagnetic** or **ferromagnetic** (attracted to the field).  
   - If \( \chi_m < 0 \), the material is **diamagnetic** (repelled by the field).  

In simple terms, **susceptibility tells us how "responsive" a material is to electric or magnetic fields.**