# What does this subscript signify?

## Main Question or Discussion Point

I am currently taken an undergrad Optics physics course, and I am often coming across functions/derivative that have subscripts. I know what those specific symbols mean but I don't know what their relationship is suppose to be. i.e.

{(δΨ/δt)x}=ω

or

(Eor/E0i)

Related Other Physics Topics News on Phys.org
Nugatory
Mentor
You will get better answers of you can tell us more about exactly where you found these expressions and how they're being used. I and many other people here could make some good guesses, but these subscripts are often used with meanings that are only clear in context... So we need that context to give you more than guesses.

You will get better answers of you can tell us more about exactly where you found these expressions and how they're being used. I and many other people here could make some good guesses, but these subscripts are often used with meanings that are only clear in context... So we need that context to give you more than guesses.

The first expression after looking it up states that the this is the partial derivative of a wave function with respect to t, holding the x constant. Hence, I presume that he subscript here means that variable is held constant.

Nugatory
Mentor
The first expression after looking it up states that the this is the partial derivative of a wave function with respect to t, holding the x constant. Hence, I presume that he subscript here means that variable is held constant.
Seems likely...

After looking it up, and reading your reply, I think I got my answer. The textbook states that, the first expression is the partial derivative of a wave function with respect to t, holding the x constant. Hence, I presume that the subscript here means that the variable is held constant.

The second expression is the left side of one of the Fresnel equations; discussing the interaction of an electromagnetic field and the interface of two different mediums. I think the subscript means that the amplitude of the electric field is perpendicular to the interface. Not sure if more could be implied by this particular subscript.

Does that sound right?