# Homework Help: Plane Polarised Light

1. Apr 1, 2017

### FelaKuti

1. The problem statement, all variables and given/known data

In plane polarised light, the oscillations of the electric field are:

• A. in a single plane, which includes the direction of energy transfer.
B. in a single plane, which is perpendicular to the direction of energy transfer
C. in perpendicular planes, which are perpendicular to the direction of energy transfer.
D. in perpendicular planes, which include the direction of energy transfer

2. Relevant equations

None.

3. The attempt at a solution

I believe I can justify ruling out C and D as plane polarised light would only have oscillations in one plane. My knowledge is that electric fields would always oscillate perpendicular to the direction of propogation, which would give me B. But I'm told it's A, can someone point me in the right direction to understand this?

2. Apr 1, 2017

### kuruman

Draw a picture. Consider the plane containing E and the direction of energy transfer. Does it contradict what you already know?

3. May 29, 2017

### Javeria

Can you please draw it? I dont understand this question at all
This is what the examiners report says:
Question 10: Answer B was most common. Students selecting this answer were thinking of the description of transverse waves after seeing reference to ‘perpendicular’. This would work if it said ‘and are’ instead of ‘which is’, but the direction reference is to the plane, not the oscillations.

4. May 29, 2017

### kuruman

Two vectors define a plane. One vector is the electric field. What is the other vector? There is no mention of the B-field, but there is mention of the direction of energy transfer (Poynting vector). Answer A does not contradict the fact that the E-vector is perpendicular to the direction of propagation.

5. May 29, 2017

### Javeria

Got it, thank youu

6. May 29, 2017

### haruspex

I regard the term "plane polarisation" as misleading. Better is the alternative name, linear polarisation.
The oscillations of the electric field are along an axis orthogonal to the direction of travel, not really in a particular plane at all. It only looks like a plane when you plot that oscillation along the direction of travel.