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American System Physics

A Physics Toolkit

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Representing Motion

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Accelerated Motion

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Forces in One Dimension

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Displacement and Force in Two Dimensions

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Motion in Two Dimensions

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Gravitation

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Rotational Motion

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Momentum and Its Conservation

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Energy and Its Conservation

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Thermal Energy

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States of Matter

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Vibrations and Waves

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Sound

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Fundamentals of Light

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Reflection and Refraction

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Interference and Diffraction

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Electrostatics

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Electric Current and Circuits

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Magnetic Fields

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Electromagnetic Induction and Electromagnetism

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Quantum Theory and the Atom

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Solid-State Electronics

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Nuclear and Particle Physics

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Quiz

15.1 Illumination – Quiz

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Illumination American Physics quiz: free practice for American System Physics. Work through this Illumination American Physics quiz and get instant feedback on every answer. If you get stuck, review the 15.1 Illumination — Notes lesson. More practice: American System Physics — all units. Syllabus: OpenStax free science textbooks.

  • Questions count: 50
  • Passing grade: A-
  • Time limit:
Start Quiz
1.
A small lamp that behaves as a point source emits a luminous flux of 1600 lm. What is the illuminance on a surface 2.5 m away that faces the lamp?
20.4 lx
50.9 lx
81.5 lx
112 lx
2.
A floodlight rated 3200 lm lights a wall 4.0 m away. Modelling it as a point source, find the illuminance on the wall.
63.7 lx
15.9 lx
87.2 lx
119 lx
3.
A light meter held 2.0 m from a point-like lamp reads 45 lx after the background has been subtracted. What is the luminous flux of the lamp?
1131 lm
180 lm
2262 lm
0.895 lm
4.
A photographer's lux meter shows 120 lx at 1.2 m from a small studio bulb with the room lights off. Estimate the bulb's luminous flux.
1810 lm
173 lm
6.63 lm
2171 lm
5.
A reading desk needs an illuminance of 50 lx. At what distance from a 1800 lm point-like lamp should the desk surface be placed?
1.69 m
2.86 m
5.73 m
3.39 m
6.
A reader moves her book lamp from 2.0 m away to 1.0 m away. How does the illuminance on her page change?
twice as large
one quarter
four times as large
half as large
7.
A potted plant is moved from 1.5 m to 6.0 m away from its grow-lamp. The illuminance on its leaves becomes what fraction of the original?
one quarter
one eighth
four times as large
one sixteenth
8.
What is the luminous intensity of a point source whose luminous flux is 2000 lm?
159 cd
25133 cd
318 cd
637 cd
9.
The distance from the Moon to Earth is about 3.84 × 10⁸ m. How long does light take to travel this distance?
1.15 × 10¹⁷ s
1.28 s
0.0213 s
0.781 s
10.
A star is 4.2 light-years away. Using c = 3.00 × 10⁸ m/s and 1 year = 3.156 × 10⁷ s, how far away is the star?
1.26 × 10⁹ m
4.54 × 10¹² m
3.98 × 10¹⁶ m
2.25 × 10¹⁵ m
11.
Light of wavelength 650 nm travels in a vacuum. What is its frequency?
4.62 × 10⁵ Hz
195 Hz
4.62 × 10¹¹ Hz
4.62 × 10¹⁴ Hz
12.
Light travels at about 2.0 × 10⁸ m/s in glass. How long does it take to cross a glass block 0.50 m thick?
1.67 ns
2.50 ns
0.100 ns
5.00 ns
13.
A science display sorts materials by how they transmit light. Which material has been sorted correctly?
Clear glass — opaque
Brick — translucent
Wood — transparent
Wax paper — translucent
14.
Each photometric quantity has its own SI unit. Which quantity is given the right unit?
Luminous intensity — candela (cd)
Illuminance — lumen (lm)
Luminous flux — lux (lx)
Luminous flux — candela (cd)
15.
Objects are either luminous or merely illuminated. Which object has been classified correctly?
Book — luminous
Candle flame — luminous
Sun — illuminated
Moon — luminous
16.
Which pairing of change and effect on illuminance (point source) is correct?
Distance halved — illuminance halves
Flux doubled — illuminance quadruples
Distance tripled — illuminance becomes one ninth
Distance doubled — illuminance halves
17.
During an eclipse both dark and partly dark regions form on Earth. Which region is described correctly?
Umbra — partial shadow
Penumbra — region of total darkness
Umbra — fully lit region
Penumbra — partial shadow, only some of the source blocked
18.
The table shows illuminance readings E at distances r from a lamp (background already subtracted). Which statement best describes the data?
E × r² is roughly constant (about 128 lx m²), consistent with the inverse-square law
E × r is constant, so E is inversely proportional to r
E decreases linearly with r
E is independent of r beyond 1 m
19.
Using the data in the table, where E × r² ≈ 128 lx m² for every row, estimate the luminous flux of the lamp.
128 lm
1608 lm
3217 lm
10.2 lm
20.
A student tests the inverse-square law. Which reading in the table is anomalous?
r = 0.40 m, E = 625 lx
r = 1.20 m, E = 69 lx
r = 1.00 m, E = 150 lx
r = 1.60 m, E = 39 lx
21.
In the table, E × r² is not constant, and it increases at larger distances. The meter reads 12 lx with the lamp switched off. What is the best explanation and fix?
The lamp flux increases with distance; use a brighter lamp
The inverse-square law fails beyond 1 m; ignore those points
The metre rule is too long; use a shorter ruler
Background light adds a constant 12 lx; subtract it from every reading before testing E ∝ 1/r²
22.
The graph shows illuminance E plotted against 1/r² for a lamp. The best-fit line has a gradient of about 80 lx m². What is the luminous flux of the lamp?
Dr Dabour Hub Academy - figure 1
80.0 lm
1005 lm
6.37 lm
503 lm
23.
What does the straight line through the origin on the graph of E against 1/r² show?
Dr Dabour Hub Academy - figure 2
E is directly proportional to r²
E is independent of distance
E is directly proportional to 1/r², confirming the inverse-square law
The lamp is an extended source
24.
In the diagram, an extended lamp illuminates an opaque object in front of a screen. Which region is the umbra?
Dr Dabour Hub Academy - figure 3
A
C
Both A and C
B
25.
The diagram shows a point source. If the point source is replaced by a long fluorescent tube, what happens to the shadow on the screen?
Dr Dabour Hub Academy - figure 4
The shadow disappears completely
A penumbra appears around a smaller central umbra
The shadow becomes one uniform umbra with sharper edges
The shadow becomes larger and entirely penumbra with no umbra ever
26.
Using the graph of illuminance against distance, what illuminance would be expected at 5 m?
Dr Dabour Hub Academy - figure 5
10 lx
32 lx
1.6 lx
6.4 lx
27.
In the diagram, a very small lamp casts a shadow S of a ball. What type of shadow is S?
Dr Dabour Hub Academy - figure 6
Umbra only, with sharp edges
Penumbra only
No shadow forms
A mixture with a wide penumbra
28.
The graph shows E against 1/r² for a lamp. Using gradient = P/(4π), what is the luminous flux P?
Dr Dabour Hub Academy - figure 7
About 38 lm
About 12 lm
About 120 lm
About 1500 lm
29.
In the set-up shown, why should the background reading with the lamp off be subtracted?
Dr Dabour Hub Academy - figure 8
To remove light from other sources so only the lamp is measured
To calibrate the metre rule
To make readings larger
It is not needed
30.
Use the table. Which material is translucent?
Brick
Air
Wax paper
Clear glass
31.
Use the table. What is the luminous intensity of a 2512 lm point source?
200 cd
2512 cd
31 cd
800 cd
32.
Use the table. Which lamp gives the greatest illuminance at 2 m?
All equal
Lamp Z
Lamp Y
Lamp X
33.
Use the table. How long does light take to travel 9.0 x 108 m in a vacuum?
27 s
9.0 s
3.0 s
0.33 s
34.
A light meter is moved from 1.0 m to 3.0 m from a point source. The new illuminance is ____ of the original. Which option completes the statement?
one third
one ninth
three times as large
one sixth
35.
Green light of frequency 5.45 × 10¹⁴ Hz has a vacuum wavelength of _____.
550 nm
5505 nm
55.0 nm
1.82 × 10⁶ nm
36.
The rate at which visible light energy is emitted by a source is called the _____.
luminous flux
illuminance
luminous intensity
light-year
37.
The Moon is a luminous object because it shines brightly in the night sky. True or false?
True
True only at full moon
False, because the Moon only reflects sunlight
False, because the Moon emits infrared, not light
38.
Frosted glass is translucent: it transmits light but scatters it so objects behind it cannot be seen clearly. True or false?
False, because frosted glass is opaque
False, because translucent materials transmit no light
True only for red light
True
39.
Illuminance is measured in lumens, the same unit as luminous flux. True or false?
False, illuminance is measured in lux (lm/m²)
True
True only for point sources
False, illuminance is measured in candela
40.
Halving the distance between a point lamp and a page quadruples the illuminance on the page. True or false?
False, it doubles the illuminance
True
False, illuminance is independent of distance
True only if the lamp flux also halves
41.
A point source casts a shadow with a sharp edge and no penumbra. True or false?
False, a point source gives only penumbra
False, point sources cannot cast shadows
True
True only for translucent objects
42.
A student says, "Light travels at 3.00 × 10⁸ m/s in every material, including water and glass." True or false?
True
True for water but not for glass
False, light is faster in glass than in a vacuum
False, light is slower in materials such as water and glass
43.
Being unable to see round a corner is evidence that light travels in straight lines in a uniform medium. True or false?
True
False, it shows that light is a longitudinal wave
False, it shows light slows down in air
True only in a vacuum
44.
A light-year is a unit of time equal to one year. True or false?
True
False, it is a distance, about 9.46 × 10¹⁵ m
False, it is a unit of speed
True only for starlight
45.
Replacing a 1000 lm lamp with a 2000 lm lamp at the same distance doubles the illuminance on a desk. True or false?
False, it quadruples the illuminance
False, the illuminance halves
True
True only if the distance also doubles
46.
Rømer made the first estimate of the speed of light using delays in the eclipses of Jupiter's moon Io. True or false?
False, it was measured using a pendulum
False, Rømer used sound echoes
True, but he measured the speed of sound
True
47.
An opaque object absorbs or reflects all the light reaching it, so it casts a shadow. True or false?
True
False, opaque objects transmit most light
True only for black objects
False, only translucent objects cast shadows
48.
A point lamp giving 40 lx at 1.0 m gives 20 lx at 2.0 m. True or false?
True
False, it gives 10 lx
False, it gives 80 lx
False, it gives 5 lx
49.
A luminous object is seen because light from it enters our eyes directly. True or false?
False, luminous objects are seen only by reflected light
True only for objects hotter than the Sun
True
False, we see it because our eyes emit light
50.
In the diagram, region A is the penumbra because only part of the extended lamp is blocked from it. True or false?
Dr Dabour Hub Academy - figure 9
True
False, A is the umbra
False, A is fully lit
True only if the lamp were a point source
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Part of Fundamentals of Light — see every lesson and quiz in this unit.
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