Mandatory Experiments: Light Flashcards
ME 1: Measurement of the focal length of a concave mirror: How did the student find the approximate focal length? Why did the student find this? How was position of image found?
Found image of a distant object.
To ensure object was placed outside of focal point so real image could be formed.
Move screen until sharpest possible image is formed.
ME 1: Measurement of the focal length of a concave mirror: Why could an image not be formed when the object was close to the mirror? State three precautions that must be taken when measuring image distance. Graph adjustments and how is focal length calculated?
Object inside the focal length and virtual image formed.
Error of parallax when measuring distance with metre stick.
Measure to back of mirror
When sharpest possible image formed
1/object distance (u) on y-axis
1/image distance (v) on x-axis
Line drawn will cut y and x-axis. If values different calculate average. This value equals 1/focal length.
ME 2: Measurement of focal length of a convex lens: Why is it difficult to measure the image distance accurately? Why is it difficult to measure when object distance is small? Same graph rules and calculations as previous. If focal length is 30cm what problem arises placing object at 31cm?
Difficult to locate sharp image or determine centre of the lens.
Object inside focal length then a virtual image is produced which cannot be formed on a screen.
Image would be formed very far away and would be difficult to form a sharp image and measure image distance accurately.
ME 3: Snell’s Law: Correct method of finding refracted ray. Graph adjustments. Why is a graph more accurate than calculating angle for each pair of angles and then finding the mean? Give two reasons why a small incident angle is not used? What would be observed if angle of incidence is 0?
Draw normal in block at point of incidence.
Measure angle between normal and refracted ray with a protractor.
Sin i on y-axis and sin r on x-axis. Refractive index is slope.
Outlier can be identified.
Slope gives weighted mean.
Smaller angles give larger percentage errors.
Smaller angles are more difficult to measure
Light passes straight through, no refraction.
ME 4: Measure the Wavelength of Monochromatic Light: Describe how the angle between the two first order images was obtained?
- Locate zero order image. Note its angular position.
- Move the telescope to one side and locate the first order image. Note this angular position.
- Move the telescope to the other side and locate the first order image. Note this angular position.
- The angle of diffraction is the angle between the zero order and the first order images.
ME 4: Measure the Wavelength of Monochromatic Light: Describe effect on diffraction angle pieta when diffraction grating with less lines per mm is used. Which grating would give a more accurate value for pieta more or less lines per mm? What is observed if white light is used?
Pieta decreases.
More lines gives smaller percentage error.
Spectrum.
ME 4: Measure the Wavelength of Monochromatic Light: Which of the angular measurements are most accurate? How was a narrow beam of light produced?
n=1 sharpest image ; n=4 largest angle smallest % error.
Adjust width of slit in the collimater
ME 5: Experiment to measure refractive index of a liquid: Procedure. Accuracy. Graph adjustments. How do you know it’s a state of no parallax?
Looking from above, adjust the search pin until the image in the plane mirror is in a state of no parallax with the apparent position of the pin in the water.
Avoid small values of real and apparent depth as measuring small measurements results in greater percentage errors.
Avoid the error of parallax when measuring real and apparent depths with metre stick.
Real depth on y-axis. Apparent depth on x-axis. Slope equals refractive index.
When the observer moves his head from side to side the images stay together.
