YEAR 11 PHYSICS - UNIT 1

LIGHT - REVISION (1)

You need to know the following:

1.General information about visible light:

*speed in air or vacuum:- 3.0 x 108 ms-1

*only small part of electro-magnetic (e.m.) spectrum

*it travels in straight lines (rectilinear propagation)

e.g. shadows, solar/lunar eclipses, pinhole cameras etc..

*transfers energy - even through vacuum

*terminology:- luminous, non-luminous, transparent, translucent, opaque, transmission, absorption, reflection, umbra, penumbra

2.Reflection in general:

*distinguish between diffuse and regular reflection

*state the laws of reflection and understand terminology:- angle of incidence, angle of reflection, normal

3.Plane Mirrors:

*use the laws of reflection to locate the image of a point object or an extended object in a plane mirror

*describe the nature and position of the image in a plane mirror - upright, same size, as far behind as the object is in front, lateral inversion, virtual

*distinguish between real and virtual images

*problems involving the minimum mirror size for a person to see their entire image - has to be at least half their height

4.Curved mirrors:

*distinguish between concave and convex mirrors

*terminology:- center of curvature - C; radius of curvature - R; pole; principal axis, principal focus, aperture, focal length, f; focal plane

*use of ray diagrams to locate images in curved mirrors:- four principal rays

*image nature and position for concave mirrors

i)object outside C - image real, inverted, diminished (M < 1)

ii)object on C - image real, inverted, same size (M = 1)

iii)object b/w C and f - image real, inverted, magnified (M > 1)

iv)object on f - no image

v)object inside f - image upright, virtual, magnified (M > 1)

*image nature and position for convex mirror - always upright, virtual and magnified

5.Mirror formula:

*mirror formula:- 1/f = 1/u + 1/v; u = object distance, v = image distance, f = focal length

*magnification, M = -v/u = Hi/Ho; Ho = object height, Hi = image height

*virtual image, v, is negative

*convex mirror, f, is negative (virtual focus)

6.Spherical aberration in mirrors:

*concave mirror only focuses to an area called the caustic curve

*parabolic mirror focuses to a point

*stop down the aperture to minimise spherical aberration in a concave spherical mirror

Light Revision 1.doc