• transparent
• translucent
• opaque
• luminous

• circular
• straight
• curved
• #### 3.  What is the definition of the ray model of light?

• Light travels in a straight path and its direction can be changed by encountering a boundary.
• Objects that emit their own light.
• The rate at which a luminous source produces light energy.
• The rate at which light strikes a unit area of a surface.

• True
• False

• True
• False
• #### 6.  The illuminance of direct sunlight on Earth is about 1×1051\times10^51×105 lx. A light on a stage has an intensity in a certain direction of 5×1065\times10^65×106 cd. At what distance from the stage does a member of the audience experience an illuminance equal to that of sunlight?

• 1.4×10−1 m1.4\times10^{-1}\ m1.4×10−1 m
• 7 m7\ m7 m
• 10 m10\ m10 m
• 5×101 m5\times10^1\ m5×101 m

• True
• False

• 27 cd
• 45 cd
• 130 cd
• 210 cd
• #### 9.  In 1987 a supernova was observed in a neighboring galaxy. Scientists believed the galaxy was 1.66×10211.66\times10^{21}1.66×1021 m away. How many years prior to the observation did the supernova explosion actually occur?

• 5.53×103 y5.53\times10^3\ y5.53×103 y
• 1.75×105 y1.75\times10^5\ y1.75×105 y
• 5.53×1012 y5.53\times10^{12}\ y5.53×1012 y
• 1.74×1020 y1.74\times10^{20}\ y1.74×1020 y
• #### 10.  What is the definition of luminous flux?

• Light travels in a straight path and its direction can be changed by encountering a boundary
• Objects that emit their own light
• The rate at which a luminous source produces light energy
• The rate at which light strikes a unit area of a surface
• #### 11.  We can see through a surface only if it

• transmits light
• absorbs light
• reflects light
• #### 12.  Objects that can be seen due to light reflecting from them are called

• Luminous flux
• Luminous sources
• Illumminate sources
• Power sources
• #### 13.  In order to see an object, the object must ______.

• reflect light towards your eyes
• send (emit or reflect) light towards your eyes
• absorb light
• transmit light
• #### 14.  The units for luminous flux, illuminance and luminous intensity, respectively, are

• lumen, candela and lux
• lux, candela and lumen
• candela, lux and lumen
• lumen, lux and candela
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