Jorun tilts a concave mirror toward the Sun and holds her palm in front of it. A small bright spot forms on her skin 10 cm from the mirror, and it is hot.
Sunlight arrives as beams that run parallel to one another. This lesson names the point where a concave mirror brings them together, and the length that goes with it.
Sunlight reaches the mirror as parallel beams.
After reflection, the beams do not stay parallel: they all pass through one point in front of the mirror.
The beams arrive parallel to the principal axis, and the point where they meet after reflection sits on the principal axis.
Jorun's bright spot is the focal point of her mirror. The spot sits 10 cm from the mirror, so the mirror has a focal length of 10 cm.
A different concave mirror brings the parallel beams together at a different distance, so each mirror has its own focal length.
Katla focuses the Sun's beams with a concave mirror. The smallest bright spot forms 20 cm from the mirror. What is the mirror's focal length?
The bright spot is where the beams arriving parallel to the principal axis meet after reflection: the focal point.
The focal length is the distance from the mirror to the focal point.
That distance is 20 cm.
The mirror has a focal length of 20 cm.
Lennart's concave mirror has a focal length of 5 cm. Parallel beams arrive parallel to its principal axis. Where do the reflected beams meet?
Beams arriving parallel to the principal axis reflect through the focal point.
The focal point sits on the principal axis, 5 cm in front of the mirror.
The reflected beams meet at the focal point, 5 cm in front of the mirror, on its principal axis.
Beams of sunlight arrive at a concave mirror parallel to its principal axis. What happens to them after reflection?
Ivor focuses sunlight with a concave mirror held 85 cm from his classroom window. The smallest bright spot forms 12 cm in front of the mirror. Enter the mirror's focal length, in cm.
Lennart says: 'The focal point of a concave mirror sits on its principal axis.' Is Lennart correct?
Which arriving beams define the focal point of a concave mirror?
A concave mirror 6 cm across has a focal length of 8 cm. Katla points it at the Sun. How far in front of the mirror does the smallest bright spot form? Enter the distance, in cm.
Which of the following states what the focal length of a concave mirror is?