Lenses Flashcards
Describe the action of a thin converging lens on a parallel beam of light.
A thin converging lens bends a parallel beam of light inward, causing the rays to converge at a point called the focal point.
Describe the action of a thin diverging lens on a parallel beam of light.
A thin diverging lens bends a parallel beam of light outward, causing the rays to spread apart as if they originate from a focal point behind the lens.
Define ‘focal length’.
The focal length is the distance between the center of the lens and the focal point, where parallel rays converge or appear to diverge.
Define ‘principal axis’.
The principal axis is the straight line passing through the center of the lens and the two focal points.
Define ‘principal focus’ (focal point).
The principal focus is the point on the principal axis where rays parallel to the axis converge (for a converging lens) or appear to diverge from (for a diverging lens).
State the difference between real and virtual images formed by lenses.
A real image is formed by converging rays and can be projected onto a screen, while a virtual image is formed by diverging rays and cannot be projected.
Draw and describe a ray diagram showing the formation of a real image by a converging lens.
A ray passing parallel to the principal axis refracts through the focal point. A ray passing through the center of the lens continues straight without bending. The rays meet to form a real image on the other side of the lens.
Draw and describe a ray diagram showing the formation of a virtual image by a converging lens.
A ray passing parallel to the principal axis refracts through the focal point. A ray passing through the center of the lens continues straight without bending. The rays diverge, and the virtual image is formed by extending the rays backward.
Define linear magnification.
Linear magnification is the ratio of the image length to the object length.
State the formula for linear magnification.
Linear magnification = image length / object length.
Describe how a single lens is used as a magnifying glass.
A converging lens is used to produce a magnified virtual image of an object by placing the object within the focal length of the lens.
Alternate-style question: How can you experimentally determine the focal length of a converging lens?
Focus parallel sunlight onto a piece of paper using the lens. Measure the distance between the lens and the paper when the smallest, brightest point of light appears. This distance is the focal length.
Draw and describe a ray diagram showing the formation of images in the normal eye.
Parallel rays entering the eye converge on the retina due to the focusing action of the eye’s lens, forming a sharp image.
Draw and describe a ray diagram showing the formation of images in a short-sighted eye.
In a short-sighted (myopic) eye, parallel rays converge in front of the retina, causing distant objects to appear blurry.
Draw and describe a ray diagram showing the formation of images in a long-sighted eye.
In a long-sighted (hyperopic) eye, parallel rays converge behind the retina, causing nearby objects to appear blurry.
