A student investigates the position of an image in a plane mirror using a ray-trace sheet.
The student draws a mirror line MR MR\,MR and a normal line NL NL\,NL perpendicular to it at point BBB. She draws an incident ray line AB AB\,AB at an angle of incidence i=35∘i = 35^\circi=35∘ to the normal. She places two pins, P1 P_1\,P1 and P2P_2P2, on the line AB AB\,AB to define the incident ray.
(i) State a practical guideline for the minimum separation distance between pin P1 P_1\,P1 and pin P2 P_2\,P2 to ensure an accurate ray trace, and explain why a larger separation is preferred.
The student views the images of pins P1 P_1\,P1 and P2 P_2\,P2 in the mirror. She places two pins, P3 P_3\,P3 and P4P_4P4, on the other side of the normal so that they align with the images of P1 P_1\,P1 and P2P_2P2. She then repeats this with a different angle of incidence i=45∘i = 45^\circi=45∘, using pins P5 P_5\,P5 and P6 P_6\,P6 to trace the second reflected ray.
(i) Describe how the student uses the lines drawn through P3,P4 P_3, P_4\,P3,P4 and P5,P6 P_5, P_6\,P5,P6 to locate the position of the virtual image Y Y\,Y of the object.
The student measures the perpendicular distance a a\,a from the object pin P1 P_1\,P1 to the mirror line MR MR\,MR as a=7.2 cma = 7.2\text{ cm}a=7.2 cm. She then measures the perpendicular distance b b\,b from the virtual image point Y Y\,Y to the mirror line MR MR\,MR as b=7.4 cmb = 7.4\text{ cm}b=7.4 cm.
(i) State whether these measurements support the theory that the image formed in a plane mirror is at the same distance behind the mirror as the object is in front of it. Justify your statement, taking typical experimental uncertainty into account.
Suggest two physical sources of inaccuracy in this pin-tracing experiment, other than human error in reading a standard ruler.
216 exam-style questions on CIE IGCSE Physics 3.2 Light, covering 3.2.1a Reflection of light, 3.2.1b Images in a plane mirror, 3.2.2 Refraction of light, 3.2.2a Refraction of light, 3.2.2b Total internal reflection, 3.2.2c Refractive index and critical angle, 3.2.2d Optical fibres, 3.2.3a Converging and diverging lenses, 3.2.3b Ray diagrams and the nature of images, 3.2.3c Virtual images and the magnifying glass, 3.2.3d Correcting long-sightedness and short-sightedness, and 3.2.4 Dispersion of light. Each one has a worked solution and a mark scheme showing where the marks go.