Download Chap. 23 Conceptual Modules Giancoli

ConcepTest 7.2a
Mirror I
mirror
An observer at point O is facing a
mirror and observes a light source
S.
c
O
Where does the observer
perceive the mirror image of the
a
source to be located?
S
b
d
ConcepTest 7.2a
Mirror I
mirror
An observer at point O is facing a
mirror and observes a light source
S.
c
O
Where does the observer
perceive the mirror image of the
a
source to be located?
S
b
Trace the light rays from the object
to the mirror to the eye. Since the
brain assumes that light travels in a
straight line, simply extend the rays
back behind the mirror to locate the
image.
Follow-up: What happens when the observer starts moving
toward the mirror?
d
ConcepTest 7.2b
You stand in front of a
mirror. How tall does the
mirror have to be so that
you can see yourself
entirely?
Mirror II
a) same as your height
b) less than your full height but
more than half your height
c) half your height
d) less than half your height
e) any size will do
ConcepTest 7.2b
You stand in front of a
mirror. How tall does the
mirror have to be so that
you can see yourself
entirely?
Mirror II
a) same as your height
b) less than your full height but
more than half your height
c) half your height
d) less than half your height
e) any size will do
Trace the light rays from the
image’s foot to the mirror and then
to the eye. Since we know that qi
= qr , you need a mirror only half
your size.
ConcepTest 7.2c
Mirror III
a) No.
Does this depend on your
distance from the mirror?
b) Yes.
c) Depends on the mirror.
d) Depends on the person.
ConcepTest 7.2c
Mirror III
a) No.
Does this depend on your
distance from the mirror?
b) Yes.
c) Depends on the mirror.
d) Depends on the person.
The further you step back, the
smaller the incident and
reflected angles will be. But the
rays will still be reflected at the
same points, so the ray from the
foot will still be reflected at midheight.
ConcepTest 7.3 All Smoke and Mirrors
You hold a hand mirror 0.5 m in
front of you and look at your
reflection in a full-length mirror 1 m
behind you. How far in back of
the big mirror do you see the image
of your face?
a) 0.5 m
b) 1.0 m
c) 1.5 m
d) 2.0 m
e) 2.5 m
1.0 m
0.5 m
ConcepTest 7.3 All Smoke and Mirrors
You hold a hand mirror 0.5 m in
front of you and look at your
reflection in a full-length mirror 1 m
behind you. How far in back of
the big mirror do you see the image
of your face?
The image of the face reflected in the
small mirror appears 0.5 m behind the
small mirror. This image (which is the
object for the big mirror) is 2.0 m
away from the big mirror. The final
image is 2.0 m behind the big mirror.
a) 0.5 m
b) 1.0 m
c) 1.5 m
d) 2.0 m
e) 2.5 m
1.0 m
0.5 m
ConcepTest 7.4 Fire and Mirrors
You want to set fire to a pile of dry
leaves. Which of these mirrors is
the best tool:
a) Flat Mirror
b) Concave Mirror
c) Convex Mirror
ConcepTest 7.4 Fire and Mirrors
You want to set fire to a pile of dry
leaves. Which of these mirrors is
the best tool:
a) Flat Mirror
b) Concave Mirror
c) Convex Mirror
The concave mirror, or converging
mirror is the only one that will work.
This mirror focuses light from the
Sun into a small point and causes the
leaves to heat up.
Follow-up: What type of lens is best for this purpose?
ConcepTest 7.5 What mirror is this?
These folks are looking into a
mirror. Based on the image, which
of these is true about the mirror
and image?
a) Concave, real
b) Concave, virtual
c) Convex, real
d) Convex, virtual
e) Flat, virtual
ConcepTest 7.5
What mirror is this?
These folks are looking into a
mirror. Based on the image, which
of these is true about the mirror
and image?
a) Concave, real
b) Concave, virtual
c) Convex, real
d) Convex, virtual
e) Flat, virtual
Because the image is bigger than the
object, the mirror can be neither flat
or convex. For flat mirrors, M=1, and,
for convex, M<1. Therefore, the
mirror must be concave. The image
is virtual because it is upright (so
q<0).
ConcepTest 7.6 Glass
What is the focal length of a pane
of window glass?
a) Zero
b) Infinity
c) Thickness of the glass
d) Impossible to
determine
ConcepTest 7.6 Glass
What is the focal length of a pane
of window glass?
a) Zero
b) Infinity
c) Thickness of the glass
d) Impossible to
determine
The focal length of the glass is
infinity. The focal length of a lens is
½ of its radius. The flat glass is like a
really big sphere with a radius of
infinity.
ConcepTest 7.7 Aberrations
A curved mirror surface can have:
a) spherical aberration
b) chromatic aberration
c) both spherical
aberration and
chromatic aberration
ConcepTest 7.7 Aberrations
A curved mirror surface can have:
Curved mirrors do not exhibit
chromatic aberration because the light
is not traveling through the glass
medium. Chromatic aberration is due
to the wavelength dependence of the
index of refraction.
a) spherical aberration
b) chromatic aberration
c) both spherical
aberration and
chromatic aberration
ConcepTest 7.8 Cameras
A camera can be modeled as a simple
converging lens that focuses an image
on the film, acting as the screen. A
camera is initially focused on a distant
object. To focus the image of an object
close to the camera, the lens must be
_____.
a) Moved away from the
film
b) Moved toward the film
c) Left where it is.
ConcepTest 7.8 Cameras
A camera can be modeled as a simple
converging lens that focuses an image
on the film, acting as the screen. A
camera is initially focused on a distant
object. To focus the image of an object
close to the camera, the lens must be
_____.
a) Moved away from the
film
b) Moved toward the film
c) Left where it is.
When the object is far away, the image is at the focal point.
When the object is brought closer to the lens (but outside f),
the image is behind the focal point.
ConcepTest 7.9 Age
Does your bathroom mirror show you
older or younger than you actually
are? Compute an order-of-magnitude
estimate for the age difference, based
on data that you specify.
a) 10-12 seconds older
b) 10-9 seconds older
c) Same age
d) 10-12 seconds younger
e) 10-9 seconds younger
ConcepTest 7.9 Mirror of Youth
Does your bathroom mirror show you
older or younger than you actually
are? Compute an order-of-magnitude
estimate for the age difference, based
on data that you specify.
a) 10-12 seconds older
b) 10-9 seconds older
c) Same age
d) 10-12 seconds younger
e) 10-9 seconds younger
Assume the mirror is 1 meter
away from you. This image that
you see in the mirror is from light
that left your body some time ago.
That time is t=d/v=2m/3x108 m/s ~
10-9 s