**5th year homework.**

**Light:**

**Light:**

**Section 1. Plane mirrors**

**Q1. Draw a diagram of how a ray of light enters and leaves a plane mirror.**

**Q2. If a person is 2.5 m from a plane mirror how far is the persons image from them?**

**Q3. If a person is approaching a mirror at a speed of 1m/s how fast is their image travelling?**

**Q4. State the laws of reflection.**

**Q5. Define light.**

**Section 2. Spherical mirrors**

**Q1. Draw a diagram of a concave mirror.**

**Q2. What is a real image?**

**Q3. what is a virtual image?**

**Q4. What is meant by parallax error?**

**Q5. What fromula would you use in order to solve problems involving concave mirrors?**

**Section 3. Spherical mirrors**

**Q1. With regard to a concave mirror, what conditions are needed to form**

**1. A real image 2. A virtual image 3. an image at infinity?**

**Q2. Draw two ray diagrams**

**1. How a real image would be fromed in a concave mirror**

**2. How a virtual image would be fromed in a concave mirror**

**Q3. Draw the setup of the apparatus you would use to find the focal length of a concave mirror.**

**Q4. When doing an experiment to find the focal length of a concave mirror the student found a approximate focal length.**

**How did the student do this**

__AND__why did the student do this?**Q5. Draw a sketch of the graph a student would expect to get when graphing the results of this experiment.**

**What is the significance of where the line cuts both the X and Y axis on the graph?**

**Section 4. Spherical mirrors**

**Q1. if the focal length of a concave mirror is 50cm and an object is placed at a distance of 65cm, what kind of image is formed? why?**

**Q2. If the object distance u =20cm and the image distance v = 15 cm for a concave mirror what is the mirrors focal length?**

**Q3. An object is placed 23cm in front of a concave mirror. the imege appears 20cm from the mirror. what will the magnification of the object be?**

**Q4. An object is 50cm high and the image it produces in a convex mirror is 10cm high. What is the magnification of the object?**

**Q5. A convex mirror has an object placed in front of it at a distance of 25cm, an image is produced in the mirror at a distance of 15cm. Find the focal length of the mirror. Find also the magnification of the object. What is the nature of the image in question?**

**Section 5. Spherical mirrors**

**Q1. A concave mirror with a focal length of 50cm produces an image which is x2 times the size of the object.**

**Find two positions where an object could be placed in front of the mirror for which this could occur. for each position you have found state the nature of the image produced.**

**Q2. A student uses a convex mirror of focal length 35cm to produce an image.**

**What can you automatically say about this image?**

**If the student then produced an image in the mirror which was x1/3 the size of the object, where would the student have to place the object in order for this to occur?**

**Section 6: Lenses**

**Q1. Explain with the aid of a diagram how you would carryout an experiment to find the focal length of a convex lens.**

**Q2. An object is placed 40cm in front of a concave lens of focal length 20cm. Find the position and nature of the image.**

**Q3. A lens has a power of 15 m ^{-1}, find its focal length.**

**Q4. Two lenses of power 20 m ^{-1} each are placed in contact. What is their combined power?**

**Q5. Two convex lenses are placed in contact with each other. Each lens has a focal length of 20cm. Find their combined focal length.**

**Q6.Two lenses one convex and the other concave are placed in contact. They have focal lengths of 20cm and 40cm respectively. Find their combined focal length.**

**Q7. Explain long and short sightedness.**

**Q8. Name and explain the function of the four main parts of the eye.**

**Section 7: Lenses**

**Q1. Give another name for a converging lense and a diverging lense.**

**Q2. An object is placed in front of a convex lense and produces an image which is X3 times the size of the object. find two positions for which this situation could occur if the focal length of the mirror is 30cm.**

**Q3. What is meant by the term accommodation of the eye?**

**Q4. Two lenses one a convex of power 50m**

^{-1}and another concave of power 50m^{-1}. What is the power of the combination?**Q5. Two concave lenses are placed in contact. one has power 10m**

^{-1}and the other has power 25m^{-1}. Find the power of the combination.**Q6. Two lenses a concave of power 26m**

^{-1}and a concave of power 12m^{-1}are in contact. find the overall power of the combination.**Section 8: Lenses**

**Q1. If a lense has a focal length of 30cm what is the power of that lense?**

**Q2. If a lense has power of 5m**

^{-1}what is the focal length of that lense?**Q3. An eye needs power of 50m**

^{-1 }in order to see correctly if a persons lenses has power of 36m^{-1}, what power lense will the person need in order to see properly? What kind of lense will the person need?**Q4. An eye nedds a power of 64m**

^{-1}in order to function correctly. If a persons eye has a lense with power of 69m^{-1}, what power lense will the person need in order to see correctly? What type of lense would you reccommend?**Q5. What is meant by the term accommodation of the eye?**

**Section 9: Refraction**

**Q1. Define refraction.**

**Q2. Why does light refract?**

**Q3. State the laws of refraction.**

**Q4. What is meant by the critical angle with regard to refraction?**

**Q5. Explain total internal reflection and give an application of it.**

**Section 10. Refraction**

**Q1. Give four different formulae that could be used to find the refractive index of a transparent substance.**

**Q2. If the angle of incidence for a ray of light is 30 degrees and the refracted ray angle is 24 degrees what is the refractive index of the substance?**

**Q3. Find the refractive index of a pool which has a depth of 2m but looks like it is only 1.75m in depth.**

**Q4. If the speed of light in air is 3x10**

^{8}ms^{-1}and its speed is slowed to 2X10^{8 }m\s when it enters a sheet of glass, what is the refractive index of the glass?**Q5. If the critical angle for a substance is 42 degrees find its refractive index.**

**Q6. If the refractive index of a glass block is 1.5 find the angle of refraction if an incident ray of light has an anlge of 45 degrees.**

**Section 11. Refraction**

**Q1. State Snell's law.**

**Q2. Give a formula for Snell's law.**

**Q3. Explain the term Snell's window.**

**Q4. A light is placed at the bottom and center of a circular pond. The depth of the pond is 4m. The refractive index of water is 1.33. Viewing from above a person sees a circular disk of light on the top of the pond. Find the diameter fo the disk of light.**

**Q5. A diver is at a depth of 10m in the sea, he looks up and sees a circle of light at the surface above him. The refractive index of seawater is 1.4. Find the diameter of the circle of light.**

**Section 12. Refraction**

**Q1. If the refractive index of a glass block is 1.5 from air to the glass, what is the refractive index from glass to air?**

**Q2. A ray of light passes from water into air the refractive index is 0.85 what is the refractive index of air to water?**

**Q3. if the refractive index from water to glass is 1.1 what is the refractive index from glass to water?**

**Q4. Refering to the Normal, what happems to a ray of light as it passes from a dense into a less dense medium?**

**Q5. The refractive index of water is 1.35, A student looks into a pool of water and says that the pool looks like it is 1.5m deep. How deep is the water in actual fact?**

**Section 13. Wave nature of Light.**

**Q1. What is meant by the term monochromatic light?**

**Q2. Define light.**

**Q3. Describe the make up of a diffraction grating.**

**Q4. What does a diffraction grating do?**

**Q5. Define diffraction.**

**Section 14. Wave Nature of Light.**

**Q1. What are the 4 properties that a phenomenon must display in order to be considered to be a wave?**

**Q2. How was it eventually shown that light is a wave? You can use a diagram to help you explain this.**

**Q3. For your answer to Q2 you should have described an experiment what was this experiment known as?**

**Q4. For the four properties you have described in Q1, explain what each property means with regard to light waves.**

**Q5. If a diffraction grating has 600 lines per mm on it find d the grating constant for this diffraction grating.**

**Section 15.**

**Q1. How many lines is there per meter on a diffraction garting with 150 lines per mm?**

**Q2. If a diffraction grating has 300 lines per mm what is the diffraction grating constant d?**

**Q3. Describe how you would set up a spectrometer in order to find the wavelength of a light source.**

**Q4. Draw a diagram of a spectrometer and explain the function of all the parts you have labelled.**

**Q5. Why does a light wave diffract through a diffraction grating but it doesnt diffract when passing through another gap such as a doorway?**

**Section 16.**

**Q1. If a diffraction grating has 500 lines per mm and the angle from the zero order image to the first order fringe is 23 degrees, find the wavelength of the light.**

**Q2. If a diffraction grating has 400 lines per mm and the angle from the first order fringe to the left to the first order fringe on the right is 40 degrees find the wavelength of the light.**

**Q3. A diffraction grating with 200 lines per mm creates an angle of 32 degrees from the zero order image to the second order fringe on the right. What is the wave length of the light?**

**Q4. An angle of 46 degrees is produced from the second order image on the left to the second order image on the right when a diffraction grating of 800 lines per mm is used. find the wavelength of the light.**

**Q5. A 90 degree angle is measured from the third order fringe on the left to the third order fringe on the right when a diffraction grating of 550 lines per mm is set up on a spectrometer. Find the wavelength of the light.**

**Section 17.**

**Q1. When carrying out an experiment to find the wavelength of a light source why was a monochromatic light source used instead of a regular bulb?**

**Q2. Explain why the electromagnetic spectrum is laid out the way it is.**

**Q3. If a diffraction grating of 600 lines per mm is used to find the wavelength of light and the result for the wavelength is 689nm. What is the maximum number of fringes the student could have seen using the apparatus?**

**Q4. The wavelength of a monochromatic light source turns out to be 900nm when a diffraction garting of 700 lines per mm is used. How many fringes max could the student have detected when carrying out the experiment?**

**Q5. Explain Young's double slit experiment which proved that light wave interfere with eachother both constructively and destructively ultimately proving that light does in fact travel as a wave.**