MCAT Physics Notes and Concepts- Reflection and Optics

An object is at a distance of 77 cm from a concave mirror with a focal length of 26 cm. What is the image distance (in cm) for this lens? Is the image inverted or upright? Is the image real or virtual? (A) 57.32 (B) 39.25 (C) -39.25 (D) -57.32

(B) 39.25 1/f = 1/o + 1/i 1/26 = 1/77 + 1/i i = approx. 40 (actual: 39.25) The image distance is 39.25 cm. The image is inverted and real. NOTE: You can use the thin lens equation, but I find that it is much easier to simply draw it out and estimate the answer since exact numbers are not a requirement on the MCAT.

An object is at a distance of 30 cm from a convex lens with a focal length of 20 cm. What is the image distance (in cm) for this lens? Is the image inverted or upright? Is the image real or virtual? (A) 90 (B) 60 (C) -60 (D) -90

(B) 60 1/f = 1/o + 1/i 1/20 = 1/30 + 1/i i = 60 The image distance is 60 cm. The image is inverted and real. NOTE: You can use the thin lens equation, but I find that it is much easier to simply draw it out and estimate the answer since exact numbers are not a requirement on the MCAT.

If an object is on the same side of a lens as the image, this is considered to be a ________ image. If an object is on the opposite side of a lens as the image, this is considered to be a ________ image. (A) virtual, virtual (B) virtual, real (C) real, real (D) real, virtual

(B) virtual, real If an object is on the same side of a lens as the image, this is considered to be a virtual image. If an object is on the opposite side of a lens as the image, this is considered to be a real image.

An object is at a distance of 20 cm from a convex mirror with a focal length of 10 cm. What is the image distance (in cm) for this lens? Is the image inverted or upright? Is the image real or virtual? (A) 18.33 (B) 6.67 (C) -6.67 (D) -18.33

(C) -6.67 1/f = 1/o + 1/i 1/-10 = 1/20 + 1/i i = approx. -7 (actual: -6.67) The image distance is -6.67 cm. The image is upright and virtual. NOTE: You can use the thin lens equation, but I find that it is much easier to simply draw it out and estimate the answer since exact numbers are not a requirement on the MCAT.

The index of refraction of a vacuum is...?

1

How is a Convex Parabolic Mirror useful for the headlights of your car?

A Parabolic Mirror will focus the light in a single direction, allowing you to focus your headlights only where you want them to highlight.

Converging lenses are always________(thicker/thinner) at the center. Diverging lenses are always_________(thicker/thinner) at the center.

A converging lens is always thicker at the center A diverging lens is always thinner at the center

What does a negative magnification signify? What about positive?

A negative magnification signifies an inverted image. A positive magnification signifies an upright image.

When is an image considered Upright vs. Inverted?

An image is considered to be Upright when it is above the horizonal axis/plane (the principal axis). An image is considered to be Inverted when it is below the horizonal axis/plane (the principal axis).

In terms of mirrors, distinguish between a real and virtual image.

An image is real if the light actually converges at the position of the image. An image is virtual if the light only appears to be coming from the position of the image but does not actually converge there.

Distinguish between concave and convex mirrors.

Concave: Converging mirror; center of curvature and the radius of curvature are located in front of the mirror. Convex: Diverging mirror; center of curvature and the radius of curvature are behind the mirror.

How many focal points does a lens have?

Each lens has two focal points, one on each side of the lens

True or False? Light waves that are reflected are absorbed into the second medium.

False. The light waves are not absorbed into the second medium. Rather, they bounce off the boundary and travel back through the first medium.

True or False? When light enters a medium with a different index of refraction, the wavelength and frequency both change.

False. When light enters a medium with a different index of refraction, the wavelength changes but the frequency of the light does not.

Distinguish between these cases: If the absolute value of magnification is less than one, then...? If the absolute value of magnification is greater than one, then...? If the absolute value of magnification is equal to one, then...?

If the absolute value of magnification is less than one, then the image is smaller than the object (reduced) If the absolute value of magnification is greater than one, then the image is larger than the object (enlarged). If the absolute value of magnification is equal to one, then the image is the same size as the object.

What does it mean if the image has a positive distance? Negative distance?

If the image has a positive distance, it is a real image and implies that it is in front of the mirror. If the image has a negative distance, it is a virtual image and is behind the mirror.

What is rectilinear propagation?

It describes the phenomenon that when light travels through a homogeneous medium, it travels in a straight line.

What is spherical aberration?

It is a blurring of the periphery of an image as a result of inadequate reflection of parallel beams at the edge of a mirror or inadequate refraction of parallel beams at the edge of a lens.

What is magnification? What is the equation for it?

It is a dimensionless ratio of the image distance to the object distance.

What is total internal reflection?

It is a phenomenon in which all the light incident on a boundary is reflected back into the original material.

What is the center of curvature?

It is a point on the optical axis located at a distance equal to the radius of curvature from the vertex of the mirror. In other words, the center of curvature would be the center of the spherically shaped mirror if it were a complete sphere.

What is refraction?

It is the bending of light as it passes from one medium to another and changes speed.

What is focal length?

It is the distance between the focal point and the mirror.

What is reflection?

It is the rebounding of incident light waves at the boundary of a medium.

What is the critical angle?

It occurs when the refracted angle (theta2) equals 90 degrees.

What is dispersion?

It occurs when various wavelengths of light separate from each other.

When does total internal reflection occur?

It results with any angle of incidence that is greater than the critical angle OR As light moves from a medium with a higher refractive index to a medium with a lower one

Lenses________ (reflect/refract) light while mirrors________ (reflect/refract) light.

Lenses refract light Mirrors reflect light

How do you calculate index of refraction?

Note that n is dimensionless

What is the equation for image and object distance for plane mirrors?

Or, i = -o

P is positive for a________ lens and negative for a________ lens

P has the same sign as f, so P is positive for a converging (convex) lens and negative for a diverging (concave) lens.

Chromatic aberration is predominantly seen in what type of lens?

Spherical lenses

What is chromatic aberration?

The dispersive effect when a rainbow halo is seen around images in a spherical lens.

What are lenses in contact?

They are a series of lenses with negligible distances between them.

True or False? Plane mirrors cause neither convergence nor divergence of reflected light rays.

True. Plane mirrors are flat reflective surfaces.

True or False? Plane mirrors always create virtual images.

True. This is because the light does not converge at all. Additionally, because the reflected light remains in front of the mirror but the image appears behind the mirror, the image is virtual.

How many times is light refracted when it passes through a lens?

Twice. It is refracted when it passes from air to lens refracted from lens back to air.

When light enters a medium with a lower index of refraction, it bends...?

away from the normal

What are the two types of spherical mirrors?

concave and convex

For thin spherical lenses, the focal lengths of either side of the lens are....?

equal

What equation is used to measure the power of a lens? What unit is it measured in?

f = focal length This is measured in diopters.

When the thickness of a lens cannot be neglected, the lensmaker's equation is used. What is it?

n = index of refraction r1 = radius of curvature for the first lens surface r2 = radius of curvature for the second lens surface

What is Snell's Law?

n1 and theta1 refer to the medium from which the light is coming n2 and theta2 refer to the medium into which the light is entering REMEMBER THAT ANGLES ARE MEASURED WITH RESPECT TO THE NORMAL

What is the equation for focal length of spherical mirrors?

r is the distance between center of curvature and the mirror

Any time an object is at the focal point of a converging mirror,

the reflected rays will be parallel, and thus, the image will be at infinity

What is the law of reflection?

theta 1= incident angle theta 2= reflected angle Note that both angles are measured from the normal, which is the line drawn perpendicular to the boundary of a medium. All angles in optics are measured from the normal, not the surface of the medium.

When light enters a medium with a higher index of refraction, it bends....?

toward the normal

A single diverging mirror forms only a...?

virtual, upright, and reduced image regardless of object position