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4.6 Conduction, Convection, and Radiation

Conduction: When a solid is being heated, the heat causes the solid particles to collide against each other and vibrate more vigorously. The particles closest to the heat will expand start vibrating and will hit the particles in the row above them. This will cause them to vibrate and pass the collision along to a different row.

Convection: Only takes place in fluids, gases and SOME solids such as sand. When water is heated the molecules heat up and start to rise as the warmer portions of the water are less dense and therefore, they rise. However, the particles soon sink as the cooler portions of the water are less dense.

Radiation: 

1. Objects absorb infrared radiation from the objects that surround them, and emit them. 
2. Hotter objects give out infrared radiation faster than they absorb the infrared radiation from the colder objects around them. 
3. Contrarily, colder objects will absorb infrared radiation faster than giving it out. 

Corrections for Exam

1. When the velocity is changing then we use the area underneath the graph to measure the distance.
2. The thinking distance is the distance travelled by the moving vehicle in the driver's reaction time. One factor which increases this is alcohol.
3. The Braking distance is the distance travelled by the moving vehicle after the brakes have been applied. One factor which increases this is poor condition of tires.
4. Frequency is the number of waves per second.
5. In a series circuit, the voltage is shared and the current is the same. On a parellel circuit, the voltage remains the same and the current is shared.
6. The battery and resistor are two components which affect the size of the current, other than the bulb.
7. The potential difference=subtracting the overall supply voltage with the voltage read across ONE component.
8. When i>c you get total internal reflection
9. Diffractions for short waves are usually curved whereas for long waves they are curved around the corners only.

Objective 3.17

Angle of incidence < critical angle= Total Internal reflection

Angle of Incidence=critical angle=critical angle

The critical angle for glass is 42 degrees.

Critical angle is the smallest angle of incidence for which total internal reflection occurs

3.15

Smoke box experiment

Light can be diffracted, refracted and reflected. However, during all these processes light travels in a straight line. We understood this through the smoke tank practical in which the ray of laser could be seen clearly.

During the experiment, in order to investigate reflection, a mirror was placed in the box. The laser light hit the mirror and reflected back to the way it came from therefore there were two rays of lights, one, which was being shone onto the mirror and the other, being reflected off the mirror.

A dense sheet of glass was placed before the light. When the light was shone through the glass surface, the ray changed its angle, bending slightly (refracting) once it penetrated through the glass surface.

Diffraction occurred when a slit was placed before the light. The light was shone into the slit and as it passed out of the small hole, the ray became wider.


Why do we see objects?

We see things due to light. Some objects are simply sight sources such as the sun. However, views of other objects, such as the moon, are reflected into your eye. The light hits the object and some of the light is reflected into your eye.

There are some objects which you can see through though. These objects are considered 'transparent'

On the other hand, objects which still reflect light but do not allow us to see through them are known as 'opaque'.

Angle of incidence and reflection

A mirror was placed at the bottom of a protractor and a normal was drawn across the front of the mirror.

Rays of light were shone at different angles to the normal, which was drawn across the front of the mirror. The angle of the light being shone (angle of incidence) and reflected (angle of reflection) were measured and recorded.

After we recorded our results, we found out that the angle of incidence=angle of reflection.