# Physics Q pack 63

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D

#### deleted647690

I'm confused about the definition of the normal for light ray problems. I thought it was the line perpendicular to the point at which the light ray was incident.

How is the light ray in option D "entering along the normal"?

I tried to draw out the normal lines, and I'm confused by the other answer choices

In B, it appears to me that the light ray, upon entering the ball, it bends to the right with respect to the normal (not sure if this means towards or away from the normal). Upon leaving, it appears to bend towards the normal.

In C, upon entering, it appears to bend towards the normal. Upon leaving, it again appears to bend towards the normal, so I'm not sure why this is marked as the correct answer, becaause it should bend away from the normal upon exiting.

In D, it appears to bend towards the normal both upon exiting and leaving.

So from the pictures I drew, I'm pretty confused about how to define the normal.

#### Attachments

• delayed.PNG
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• IMG_0561.JPG
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• normal.PNG
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#### Doogie.Howser

##### Full Member
2+ Year Member
To define the normal line, it's the line perpendicular to the surface of the lens/water/object/etc. that the light is entering. It does not matter how the light travels nor the angle it hits the surface of the object. Simply draw a perpendicular line coming from the object at the point of contact (again, one that's independent of the light coming in). If you still need help, let me know.

D

#### deleted647690

To define the normal line, it's the line perpendicular to the surface of the lens/water/object/etc. that the light is entering. It does not matter how the light travels nor the angle it hits the surface of the object. Simply draw a perpendicular line coming from the object at the point of contact (again, one that's independent of the light coming in). If you still need help, let me know.
Thanks, I tried redrawing the normal lines for each option, and I still don't really see how B is "bending away from the normal" upon entering the bulb. To me, it appears that it is bending to the right, and the angle between the line entering the bead and the normal is less than the angle of the line upon entering the bead, so that it is in fact bending toward the normal

#### Attachments

• IMG_0562.JPG
53.7 KB · Views: 121

#### Doogie.Howser

##### Full Member
2+ Year Member
Here is my best attempt at art. The normal lines you drew aren't correct. The line you drew is parallel to the object. You can see from my image that for B, the light bends towards the normal as it enters, and bends away from the normal as it leaves. The normal lines are drawn in green.

#### Attachments

• FullSizeRender.jpg
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D

#### deleted647690

Here is my best attempt at art. The normal lines you drew aren't correct. The line you drew is parallel to the object. You can see from my image that for B, the light bends towards the normal as it enters, and bends away from the normal as it leaves. The normal lines are drawn in green.
ah, thank you. I guess I forgot what perpendicular looked like haha

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