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Set LW4 – Illuminance vs. Distance

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Assignment Overview

Use the inverse square relationship between illuminance and distance to predict the effect that changes in distance will have upon the illuminance. 

 1. LW4Q1
Points: 0/5

Light is emitted by a light bulb at a rate of P. A light sensor is used to determine the rate at which it reaches a surface some distance of d from the surface. The sensor is measuring the illuminance (E) in units of lux. Use this information and the scaled diagram to answer the next few questions. When the sensor is placed at location A, it reads 697 lux.

  1. When the sensor is placed at location B, twice as far from the source, the sensor would read ______ lux.

    Illuminance

    lux

  2. When the sensor is placed at location C, three times as far from the source, the sensor would read ______ lux.

    Illuminance

    lux

  3. When the sensor is placed at location D, four times as far from the source, the sensor would read ______ lux.

    Illuminance

    lux

  4. When the sensor is placed at location E, five times as far from the source, the sensor would read ______ lux.

    Illuminance

    lux

  5. When the sensor is placed at location F, six times as far from the source, the sensor would read ______ lux.

    Illuminance

    lux

 2. LW4Q2
Points: 0/1

Consider two separate experiments conducted to measure the illuminance at a given distance from two different light bulbs. Light bulb A is two times as bright as light bulb B. That is, light bulb A emits light at two times the rate as light bulb B; it has two times the power or luminous flux. A sensor is used to measure the rate at which light from a source reaches a surface - i.e., the illuminance. When placed a distance of 5.01 cm from bulb A, the sensor reads 174 units of illuminance. At what distance (in cm) from bulb B will the same sensor read 174 units of illuminance?

  1. Distance from Bulb B

    cm

 3. LW4Q3
Points: 0/5

Jacobi and Dylan are using a Maglite to study the relationship between illuminance and distance. Their light sensor reports an illuminance of 355 lux a distance of 14 cm from the light source. Use the inverse square law to predict the illuminance at a distance of …. 

  1. ... 7 cm from the source.

    Illuminance

    lux

  2. ... 21 cm from the source.

    Illuminance

    lux

  3. ... 28 cm from the source.

    Illuminance

    lux

  4. ... 35 cm from the source.

    Illuminance

    lux

  5. ... 42 cm from the source.

    Illuminance

    lux


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