Question

The second harmonic of a guitar string has a frequency of 120 Hz. What is the length of the guitar string if the speed of the waves on the string is 110 m/s?


0.7 m

0.9 m

1.6 m

1.4 m

Answer 1

@ghuczek

Answer 2

What do you know about the second harmonic? What does that mean?

Answer 3

that it is half? @ghuczek

Answer 4

No, the first harmonic is half a wavelength.

Answer 5

The second harmonic is a full wavelength. There are nodes at both ends of the vibrating string and one in the middle. In other words, they are asking you to find the wavelength, which for the second harmonic is the length of the string.

Answer 6

0.9? @ghuczek

Answer 7

Yes. \( v = f \lambda\) and you solved for \(\lambda\).

Answer 8

thanks, do you know this one? @ghuczek

Two positive charges of 6 µC are separated by a distance of 50 cm in air. What is the electric field strength at the midpoint of the line joining the charges?


72.0 V/m

64.8 V/m

6.0 V/m

zero V/m

Answer 9

Both charges are positive. What happens when like charges get close together?

Answer 10

72v? @ghuczek

Answer 11

No. What would the lines of force look like between the two charges?

Answer 12

they would retract each other @ghuczek

Answer 13

They repel.

Answer 14

so zero? @ghuczek

Answer 15

Look carefully at the force in the middle. What do you notice? The force is indeed zero in this peculiar situation. Good job.

Answer 16

Thanks! last one @ghuczek
When a light passes from glass to air, which of the following is correct for the path of the light?


The path of the light is bent toward the normal.

The path of the light is bent away from the normal.

The path of the light is parallel to the normal.

The path of the light is straight without any bends.

Answer 17

This one you need to know for the final exam! When light travels to a less optically dense medium it speeds up. So which way would it bend?

Answer 18

it is refracted and changes speed @ghuczek

Answer 19

Yes it does. It travels faster in ait than in glass.

Answer 20

would it be b? @ghuczek

Answer 21

Yes indeed. The other possibility is that if the incident ray exceeds the critical angle, you could also get total internal reflection. This is not one of the choices you had, so you can assume this situation involved an incident ray smaller than the critical angle.

Good luck with the rest of your review. Bye for now ...

Answer 22

thanks :)