AQA A Level Physics Astrophysics EXAM QUESTIONS AND CORRECT VERIFIED
ANSWERS|GRADE A+ GUARANTEED
Definition of Principal focus (Focal Point) - answerThe point through which all light parallel to
the axis of the lens passes through
Definition of Focal length - answerThe distance between the centre of the lens and the focal
point.
Converging lenses - answerConvex (thicker in middle), bend light rays towards each other
Ray diagram - horizontal axis - answerPrincipal axis
Ray diagram - vertical axis - answerLens axis
Rays parallel to principal axis - answerAxial rays
Each ray is from top of the object
Separate light rays all from same position of the object
Rays that aren't parallel to the principal axis - answerNon-axial rays
Ray diagram - focal plane - answerPlane perpendicular to the principal axis, contains the
principal focus
Formation of images by converging lenses - object beyond 2f - answerReal, inverted,
diminished image
,Formation of images by converging lenses - object between 0f and 1f - answerVirtual,
upright, magnified
Formation of images by converging lenses - object at 1f - answerReal, inverted image, same
size
Formation of images by converging lenses - between 1f and 2f - answerReal, inverted,
magnified image
Ray diagram of a refracting telescope in normal adjustment - answerParallel non-axial rays
from top of object
Refracted through objective lens (thinner)
Rays meet at focal point, forming real, inverted, diminished image
Pass through eye piece lens (thicker)
Virtual, inverted, magnified image formed at infinity
Objective lens - answerConverges ray from object to form a real, inverted, diminished image
inside the telescope
Eye piece lens - answerActs as a magnifying glass on real image to form a virtual, inverted,
magnified image at infinity
Must be within 1 focal length of the real image formed inside the telescope
Angular magnification in normal adjustment - answerM = B/a = fo/fe
M = angular magnification
B- angle to image (angle subtended by image at eye)
a- angle to object (angle subtended by object at unaided eye)
fo = focal length for objective lens
, fe = focal length for eye piece lens
fo >> fe
Ray diagram of a reflecting telescope (Cassegrain arrangement) - answerAxial rays are
reflected off parabolic concave primary mirror (principal focus is behind the secondary
mirror)
Reflected onto convex secondary mirror and focused to the principal focus of the secondary
mirror through a hole in primary mirror (focus is behind primary mirror)
Refracted by eye piece lens, forming virtual, inverted, magnified image at infinity
Definition spherical aberration - lens - answerWhere parallel rays at different distances from
principal axis are brought to focus at different points (on principal axis).
Don't converge at the same point
How to solve spherical aberration - answerUse a parabolic mirror
Large mirrors of good quality are easier to make
Can be supported from underneath, so less distortion
Diagram of spherical aberration of a mirror - answerrays further from principal axis are
focused to a point closer to mirror
If mirror is not perfectly parabolic
Effect on image of spherical aberration - answerImage is blurred
Can happen at both primary and secondary mirrors
Secondary also blocks light and there is some diffraction around it
Definition chromatic aberration - answerWhere different wavelengths are refracted by
different amounts resulting in different focal lengths for different wavelengths (colours)
Blue refracted more than red
Building larger lenses of good quality is difficult and expensive
ANSWERS|GRADE A+ GUARANTEED
Definition of Principal focus (Focal Point) - answerThe point through which all light parallel to
the axis of the lens passes through
Definition of Focal length - answerThe distance between the centre of the lens and the focal
point.
Converging lenses - answerConvex (thicker in middle), bend light rays towards each other
Ray diagram - horizontal axis - answerPrincipal axis
Ray diagram - vertical axis - answerLens axis
Rays parallel to principal axis - answerAxial rays
Each ray is from top of the object
Separate light rays all from same position of the object
Rays that aren't parallel to the principal axis - answerNon-axial rays
Ray diagram - focal plane - answerPlane perpendicular to the principal axis, contains the
principal focus
Formation of images by converging lenses - object beyond 2f - answerReal, inverted,
diminished image
,Formation of images by converging lenses - object between 0f and 1f - answerVirtual,
upright, magnified
Formation of images by converging lenses - object at 1f - answerReal, inverted image, same
size
Formation of images by converging lenses - between 1f and 2f - answerReal, inverted,
magnified image
Ray diagram of a refracting telescope in normal adjustment - answerParallel non-axial rays
from top of object
Refracted through objective lens (thinner)
Rays meet at focal point, forming real, inverted, diminished image
Pass through eye piece lens (thicker)
Virtual, inverted, magnified image formed at infinity
Objective lens - answerConverges ray from object to form a real, inverted, diminished image
inside the telescope
Eye piece lens - answerActs as a magnifying glass on real image to form a virtual, inverted,
magnified image at infinity
Must be within 1 focal length of the real image formed inside the telescope
Angular magnification in normal adjustment - answerM = B/a = fo/fe
M = angular magnification
B- angle to image (angle subtended by image at eye)
a- angle to object (angle subtended by object at unaided eye)
fo = focal length for objective lens
, fe = focal length for eye piece lens
fo >> fe
Ray diagram of a reflecting telescope (Cassegrain arrangement) - answerAxial rays are
reflected off parabolic concave primary mirror (principal focus is behind the secondary
mirror)
Reflected onto convex secondary mirror and focused to the principal focus of the secondary
mirror through a hole in primary mirror (focus is behind primary mirror)
Refracted by eye piece lens, forming virtual, inverted, magnified image at infinity
Definition spherical aberration - lens - answerWhere parallel rays at different distances from
principal axis are brought to focus at different points (on principal axis).
Don't converge at the same point
How to solve spherical aberration - answerUse a parabolic mirror
Large mirrors of good quality are easier to make
Can be supported from underneath, so less distortion
Diagram of spherical aberration of a mirror - answerrays further from principal axis are
focused to a point closer to mirror
If mirror is not perfectly parabolic
Effect on image of spherical aberration - answerImage is blurred
Can happen at both primary and secondary mirrors
Secondary also blocks light and there is some diffraction around it
Definition chromatic aberration - answerWhere different wavelengths are refracted by
different amounts resulting in different focal lengths for different wavelengths (colours)
Blue refracted more than red
Building larger lenses of good quality is difficult and expensive
