What is the difference between curly and derivative (d) sign

1. Mar 19, 2015

masyousaf1

Dear All,

Please see the image below in attachment where Energy is function of K. I want to understand how is it possible to understand the last expression ( dE = ? ). Additionally, what is the difference between curly and derivative (d) sign ?

Many thanks to the mentors on this forum
Best wishes

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2. Mar 19, 2015

RaulTheUCSCSlug

the "curly" derivative (d) sign is called a partial derivative, and is when you only take derivative of a function that has multiple variables. It works very similar to a regular derivative.

3. Mar 19, 2015

RaulTheUCSCSlug

The last expression is just taking the partial derivative of E with respect to each k, and summing them up since the derivative of the sum is the sum of derivatives!

4. Mar 19, 2015

Khashishi

This subject is covered in multivariable calculus

5. Mar 20, 2015

masyousaf1

Thanks RaulTheSCSlug, kindly mention what is the physical meaning of the quantity ∂E/∂k1 * dk1 .

Best wishes