Wave Properties. Page 1 of 13

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1 Wave Properties Transverse and longitudinal waves Be able to describe the difference between longitudinal and transverse waves including examples of each (e.g. ripples / light for transverse & sound (compression waves) for longitudinal. Describe evidence that, for both ripples on a water surface and sound waves in air, it is not the wave and not the water or air itself that travels. Properties of waves Be able to describe wave motion in terms of their amplitude, wavelength, frequency and period. Amplitude maximum displacement of a point on a wave away from its undisturbed position. Wavelength distance from a point on one wave to the equivalent point on the adjacent wave. Frequency number of waves passing a point each second. Period /frequency [T= /f](equation on the physics equation sheet) Period, T, in seconds, s Frequency, f, in hertz, Hz The wave speed is the speed at which the energy is transferred (or the wave moves) through the medium. All waves obey the wave equation: Wave speed frequency x wavelength [v=f λ] (learn this equation) Wave speed, v, in metres per second, m/s Frequency f, in hertz, Hz, Wavelength, λ, in metres, m Be able to identify amplitude and wavelength from given diagrams Describe a method to measure the speed of sound waves in air and describe a method to measure the speed of ripples on a water surface. Be able to show how changes in velocity, frequency and wavelength, in transmission of sound waves from one medium to another are inter-related. Required practical be able to identify the suitability of apparatus to measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid and take appropriate measurements. Reflection of waves Be able to construct ray diagrams to illustrate the reflection of a wave at a surface Be able to describe the effects of reflection, transmission and absorption of waves at material interfaces Required practical investigate the reflection of light by different types of surfaces and the refraction of light by different substances. Lenses Be able to explain how lenses form an image by refracting light. Draw ray diagrams to illustrate similarities and differences between convex and concave lenses. Be able to identify and describe (or draw on a diagram) the principal focus (where parallel rays of light are brought to a focus) and the focal length. Recall that the image produced by a convex lens can be either real or virtual but the image produced by a concave lens is always virtual. The magnification produced by a lens can be calculated using the equation: Magnification image height / object height (this equation is on the Physics equation Page of 3

2 sheet) Magnification is a ratio and has no units. Image height and object height should both be measured in the same unit either both in mm or both in cm. You should be able to describe an experiment to investigate the magnification produced by a range of convex lenses. Independent Study Suggestions: Look at the specimen points above and make sure you understand them all and can recall the equations and how to draw the different diagrams correctly. Remember to include how to describe wavefronts, to draw diagrams using wavefronts and explain refraction using wavefront diagrams (it s possibly not clear above that you need to know how to do this). Wave motion (including wavelength, frequency, time period) FUSE school Wave properties, Transverse and Longitudinal, Reflection and refraction, lenses GCSE Bite size Properties of waves Scool Physics Page 2 of 3

3 Wave Properties Past Paper Questions Q. (a) Figure shows a ray of light entering a glass block. (i) The angle of incidence in Figure is labelled with the letter i. On Figure, use the letter r to label the angle of refraction. () Figure 2 shows the protractor used to measure angles i and r. What is the resolution of the protractor? Tick ( ) one box. degree 5 degrees 0 degrees () The table shows calculated values for angle i and angle r from an Page 3 of 3

4 investigation. Calculated values sin i = 0.80 sin r = 0.50 Use the values from the table to calculate the refractive index of the glass. Refractive index = (2) (c) A concave (diverging) lens is fitted into a door to make a security spyhole. Figure 3 shows how this lens produces an image. (i) State one word to describe the nature of the image in Figure 3. Page 4 of 3

5 () Use data from Figure 3 to calculate the magnification of the image. Magnification = (2) What is another use for a concave lens? Tick ( ) one box. A magnifying glass Correcting short sight To focus an image in a camera () (Total 9 marks) Q2. Light changes direction as it passes from one medium to another. (a) Use the correct answer from the box to complete the sentence. diffraction reflection refraction The change of direction when light passes from one medium to another is called. () (b) Draw a ring around the correct answer to complete the sentence. When light passes from air into a glass block, it changes direction away from the normal. towards the normal. to always travel along the normal. () Page 5 of 3

6 (c) Diagram shows light rays entering and passing through a lens. Diagram (i) Which type of lens is shown in Diagram? Draw a ring around the correct answer. concave convex diverging () In Diagram, what is the point X called? () (d) A lens acts like a number of prisms. Diagram 2 shows two parallel rays of light entering and passing through prism A and prism C. Diagram 2 Draw a third parallel ray entering and passing through prism B. (4) (e) What two factors determine the focal length of a lens?. 2. Page 6 of 3

7 (2) (Total 0 marks) Q3. (a) The diagram shows how a convex lens forms an image of an object. This diagram is not drawn to scale. (i) Which two words describe the image? Draw a ring around each correct answer. diminished inverted magnified real upright (2) The object is 4 cm from the lens. The lens has a focal length of 2 cm. Calculate the image distance. Image distance = cm (3) (b) What does a minus sign for an image distance tell us about the nature of the image? () (Total 6 marks) Page 7 of 3

8 Q4. A student investigates how the magnification of an object changes at different distances from a converging lens. The diagram shows an object at distance d from a converging lens. (a) (i) The height of the object and the height of its image are drawn to scale. Use the equation in the box to calculate the magnification produced by the lens shown in the diagram. magnification = Show clearly how you work out your answer. Magnification = (2) The points F are at equal distances on either side of the centre of the lens. State the name of these points. () Explain how you can tell, from the diagram, that the image is virtual. () (b) The student now uses a different converging lens. He places the object between the Page 8 of 3

9 lens and the point F on the left. The table shows the set of results that he gets for the distance d and for the magnification produced. Distance d measured in cm Magnification His friend looks at the table and observes that when the distance doubles from 0 cm to 20 cm, the magnification doubles from.5 to 3.0. His friend s conclusion is that: The magnification is directly proportional to the distance of the object from the lens. His friend s observation is correct. His friend s conclusion is wrong. (i) Explain using data from the table why his friend s conclusion is wrong. (2) Write a correct conclusion. () The maximum range of measurements for d is from the centre of the lens to F on the left. The student cannot make a correct conclusion outside this range. Explain why. Page 9 of 3

10 () (Total 8 marks) Page 0 of 3

11 Mark schemes Q. (a) (i) degree.6 allow mark for correct substitution, ie 0.80 / 0.5 provided no subsequent step shown working showing.59(9..) scores zero 2 (c) (i) any one correct description: upright virtual diminished. treat multiple words as a list 0.25 allow mark for correct substitution, ie / 4 or 5 / 20 provided no subsequent step shown ignore any unit 2 Correcting short sight [9] Q2. (a) (b) refraction towards the normal (c) (i) convex Page of 3

12 principal focus accept focal point (d) (e) parallel on left refracted towards the normal at first surface refraction away from normal at second surface passes through or heads towards principal focus refractive index accept material from which it is made (radius of) curvature (of the sides) accept shape / radius do not accept power of lens ignore thickness / length [0] Q3. (a) (i) magnified upright v = 6(cm) max 2 marks if no minus sign 6(cm) gains 2 marks /v = /2 /4 = /6 gains 2 marks /2 = /4 + /v gains mark 5.99(cm) using decimals gains 3 marks 3 (b) it is virtual [6] Q4. (a) (i) answer in the range inclusive accept for mark or or 36 2 or 37 2 or 8 6 or Page 2 of 3

13 or or or answer in the range but with a unit eg 3 cm (principal) focus / focal (point(s)) / foci / focus accept focusses accept focals do not accept focal length at the intersection of virtual / imaginary rays or where virtual / imaginary rays cross or the rays of (real) light do not cross or the image on the same side (of the lens) as the object or the image is drawn as a dotted line or the image is upright do not accept cannot be put on a screen do not accept any response which refers to reflected rays 2 (b) (i) another correct observation about relationship between values of d example 5 is three times bigger than 5 but (but) not the relationship between corresponding values for magnification 2.0 is not three times bigger than.2 when the distance / d increases the magnification increases or the converse accept there is a positive correlation do not accept any response in terms of proportion / inverse proportion (student has) no evidence (outside this range) accept data / results / facts for evidence [8] Page 3 of 3