ch6 practicals

Question 1

what is an oscilloscope

what do x and y represent

how to use to measure frquency

Answer 1

an oscilloscope shows how the potential difference across a component varies with time

the y-values shows pd, x shows time, you can change these values

connecting a signal generator produces a trace, find time period by measuring distance of one wavelenth and noting the timebase, do 1/ t to get frequency

Question 2

how to find refractive index for transparent block

Answer 2

set up as shown.

measure angle of refraction for range of angles of incidence

calculate sin i and sin r for each pair

plot on graph sin i (y) against sin r (x),gradient is refractive index

uncertainties in i and r angles will produce uncertainties in sin i and sin r, so there will be an uncertainty in the gradient and so uncertainty in the refractive index

Question 3

set up to view standing waves on a rubber cord

how to get velocity of progressive waves

Answer 3

set up apparatus as shown, making sure to stretch cord to twice its length.

use vibration generator to increase frequency until you eventually see the first standing pattern which will be the fundamental frequency, 2 nodes and an antinode in the middle

when this frquency is doubled you see the second harmonic, increasing further will give you more standing patterns

to get velocity, measure wavelength of standing wave, get frequency from generator, v = f * lambda

Question 4

how to find speed of sound in air using resonance tube

Answer 4

you can find the speed of sound in air using a resonance tube with one end in water. you need a tuning fork of known frequency

hold a tuning fork above the tube to find L1, the shortest length of tube that increases the amplitude of the sound from the tuning fork. here there will be a node at the surface and an antinode just above the tube. L1 + k (a correction) will be equal to a quarter wavelength

when there’s 3 times as much of the tube out the water, L2, the amplitude will increase. here L2 + k will give 3/4 of the wavelength

L2 - L1 = 0.5 wavelength

v = f * lambda

Question 5

how to determine wavelength of light using double slit

uncertainties

Answer 5

to determine wavelength of light using interference you need:

slit separation d, dist from slit to screen L should be few metres, fringe separation x

greatest ucnertainty is measuring slit seperation. if using diffraction grating, use number of lines per mm, * by 1000, divide by 1 to get a precise slit seperation answer

tan theta = x/L sin theta = lambda / d

small angle approximation sin theta = tan theta

x/L = lambda / d

wavelength = xd / L