Insulating materials are rated by their specific heat heat index r-value temperature resistance

Option (c) is the correct answer.

Explanation:

The difference in temperature when per unit of heat flux is required by one unit of heat flux between a barrier of warmer and colder surface present in steady state condition is known as R-value.

Mathematically,       R-value =

Thermal resistance of insulating products or materials can be known with the help of R-value. As more is the r-value of a substance more will be its insulating power.

Therefore, we can conclude that insulating materials are rated by their r-value.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

beta is electron from nucleus

something from nucleus has changed, but charge must be same for cons of charge