Physics: Light, Lenses, Wind, Motion, and Radiation
Physics: Understanding the Physical World
Light and Its Properties
Light is a form of energy that enables us to see.
- Luminous objects emit their own light. Example: Fire
- Non-luminous objects do not emit their own light but reflect light. Example: Table
Mirrors and Their Effects on Images
- Convex mirrors make images appear smaller.
- Concave mirrors make images appear larger.
- Plane mirrors produce no change in image size.
Experiment: Image Formation in a Plane Mirror
Set up the equipment as shown in the diagram. Adjust the height of the search pin so that its tip is just above the top of the mirror. Looking towards the mirrors and ignoring the object pin, you should see:
- The image in the mirror
- The search pin above the mirror
Adjust the search pin until it appears to be in line with the image. Move the search pin towards or away from the mirror until there is no parallax between the image and the search pin. The search pin then points out the position of the image. Measure the distance (u) from the object to the mirror. Measure the distance (v) from the search pin to the mirror.
Result: u = v, thus showing that the image in a plane mirror is the same distance behind the mirror as the object is in front of the mirror.
Experiment: Determining the Focal Length of a Lens
Place the lamp box well outside the approximate focal length. Move the screen until a clear, inverted image of the crosswire box is visible. Measure the distance (u) from the crosswire to the lens. Measure the distance (v) from the screen to the lens. Calculate the focal length using 1/f = 1/u + 1/v.
Repeat for different values of u. Calculate f each time and find the average.
Lens Power Calculation
1/20 = 0.05 diopters
Vision Correction
- Short-sightedness: Concave lens
- Far-sightedness: Convex lens
Wind: Causes and Effects
Wind is caused by the heating and cooling of the Earth. The heat of the sun and the rotation of the Earth cause the wind to move. Warm air expands, taking up more space. On the contrary, cool air contracts, taking up less space. This also moves the air.
Wind skate-sailing uses the motivating force of the wind, which pushes the person around using rollerblades and a sail.
When warm and cool air masses meet, hail is formed. It starts as rain, warms up and rises, which adds more moisture, then falls back down, freezes, and falls.
Motion: Speed and Velocity
- Speed = Distance / Time
- Velocity = Speed in a given direction
Experiment: Measuring the Speed of a Trolley
Set up the apparatus as shown in the diagram. Connect the ticker timer to a low-voltage power supply. Give the trolley a small push to start it moving. Adjust the runway until the trolley moves with constant speed. Most ticker timers make 50 spots per second. Therefore, the time interval between spots is 0.02 seconds. Measure the length of 10 spaces. Repeat using pushes of varying strength. Tabulate your results.
The Electromagnetic Spectrum
The electromagnetic spectrum is the range of visible and non-visible light, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
- Gamma rays are used in hospitals for sterilization.
- Microwaves are used in telephone calls.
Microwave Cooking
Microwave radiation uses heat waves to heat the water inside cells, therefore cooking the object from the inside.
Careers in Physics
There are many jobs that utilize physics.