Job 1. Sally and Kenny Go Wading.

Although the rock seemed to be 4 feet away, it was actually only 3.06 feet from Kenny's foot |

Job 3. How a prism separates blue light from red light.

In this part the given value of angle *a* can be varied. Solutions are provided for five values of this angle.

When angle "a" is | angle b(red) is | angle b(blue) is | angle "e" between red and blue ray is |
---|---|---|---|

40° | 25.20° | 24.84° | 2.24° |

45° | 27.90° | 27.50° | 1.92° |

50° | 30.50° | 30.05° | 1.75° |

55° | 32.85° | 32.37° | 1.65° |

60° | 35.00° | 34.47° | 1.59° |

Job 4. How the Human Eye Works.

Part a. In this part the given value of Ferdinand's height can be varied. Solutions are provided for four values of this height.

When Ferdinand's height is | Height of Ferdinand's Image is |
---|---|

150 cm | 0.60 cm |

160 cm | 0.64 cm |

170 cm | 0.68 cm |

180 cm | 0.72 cm |

focal length of the eye-lens when Ferdinand is 10m away is 3.98 cm |

Part b. Closest distance at which student can focus. In this part the value of the student's closest object distance may vary. Solutions are provided for five values of this distance.

When student's closest distance is | focal length of student's eye lens is |
---|---|

15 cm | 3.16 cm |

12 cm | 3.00 cm |

10 cm | 2.86 cm |

8 cm | 2.66 cm |

5 cm | 2.22 cm |

Part c. Resolving Power of the human retina. In this part the value of the farthest distance that the student can resolve the ½cm letters: RZAFLPDQ may vary. Solutions are provided for three values of this distance.

Farthest distance to read RZAFLPDQ | size of smallest image retina can resolve |
---|---|

4 meters | 0.0050 cm |

6 meters | 0.0033 cm |

8 meters | 0.0025 cm |

Part d. Size of the image of the RZAFLPDQ crater that is projected onto the un-aided human eye retina. In this part, the given value of the diameter of the crater can vary. Solutions are provided for three values of this diameter.

Given diameter of RZAFLPDQ crater | size of crater image on human eye retina |
---|---|

38 km | 0.0004 cm |

57 km | 0.0006 cm |

76 km | 0.0008 cm |

Job 5. The Telescope.

Part a. Since the object is almost infinitely far away, the image distance of the objective lens (the distance at which the infinitely far object is focused) is equal to the given value of the objective lens, or 76 cm.

Part b. In this part the student is prompted to use the same value of the crater diameter that was given to the student in Job 4 Part d. Solutions are provided for the same three values of crater diameter as in 4d.

Given diameter of RZAFLPDQ crater | diameter of "first" image in telescope |
---|---|

38 km | 0.0076 cm |

57 km | 0.0114 cm |

76 km | 0.0152 cm |

Part c.

The focal length of the combination of eye-lens and telescope eyepiece lens combination is 1.95 cm |

Part d.

The object distance from the "first image" to the eye-eyepiece combination, for good focusing, is 3.8 cm |

Part e.

Given diameter of RZAFLPDQ crater | diameter of retinal image of the crater |
---|---|

38 km | 0.008 cm |

57 km | 0.012 cm |

76 km | 0.016 cm |

Part f. Yes, your retina will distinguish craters of any of the three diameters.

Part g.

The magnification of the telescope is 20 |

Part h.

The ratio of the focal length of the objective lens to the focal length of the eyepiece lens is 20 |

This suggests that the magnification of a telescope is equal to the ratio of the focal length of the objective lens to the focal length of the eyepiece lens. This is in fact generally true, and it can be proved.

Back to Job #1: Sally and Kenny go Wading

Back to Job #2: The famous fishing pole paradox

Back to Job #3: How a prism separates blue light from red light

Back to Job #4: The World's First Camera, or, How the Human Eye Works

Back to Job #5: The Telescope, or How the Dutch Lens Grinders Made Galileo Famous

On to the Telescope Lab: Take two lenses and make a telescope right there in the lab

*Permission is hereby granted to reproduce the contents of this section for use in teaching, provided no charge or fee is accepted and provided credit is given to Cavendish Science Organization*

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