Light and Sound Flashcards
Define a luminous and non-luminous object and give examples of both. (4)
Luminous objects, like the Sun, can be seen because they produce their own light. The light travels in a straight line directly from the source to your eye. For example, a candle.
Non-luminous objects, like the Moon, do not produce their own light, but they can be seen because they reflect light from luminous objects. The light travels in a straight line directly from the object to your eye. For example, a book.
Does light travel in curved or straight lines? (1)
Straight.
Describe an experiment to prove light travels in straight lines. (2)
If you shine a torch through a small hole, the light that comes through will be in the shape of the hole, as the light that was let through went in a straight line.
Describe an experiment to show reflection. (4)
Set up a ray box, slit and lens so that a narrow ray of light is produced.
Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
Place a plane mirror against the first line.
Use the ray box to shine a ray of light at the point where the normal meets the mirror. This is the incident ray.
The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the mirror.
Using a pencil on the paper, mark the path of:
The incident ray with a cross
The reflected ray with a cross
Remove the mirror. Join the crosses to show the paths of the light rays.
Measure the angle of incidence and angle of reflection for the mirror.
Repeat steps 2 - 8 for several different angles of incidence.
Describe an experiment to show refraction. (4)
Set up a ray box, slit and lens so that a narrow ray of light is produced.
Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
Place the longest side of a rectangular acrylic polymer block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it.
Use the ray box to shine a ray of light at the point where the normal meets the block. This is the incident ray.
The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray leaving the opposite face of the block.
Using a pencil on the paper, mark the path of:
The incident ray with a cross
The ray that leaves the block with two crosses - one near the block and the other further away
Remove the block. Join the crosses to show the paths of the light rays.
Repeat steps 2 - 7 for a rectangular glass block.
Measure the angle of incidence and angle of refraction for each block.
Name the colours of dispersed white light. (2)
Red, Orange, Yellow, Green, Blue, Indigo, Violet. (From top to bottom.)
How can we see colours? How can colours can be absorbed or reflected? (3)
Our eyes only detect three colours: red, green and blue. By combining these, however, we can perceive many different colours.
By mixing red light and green light, for example, we can see yellow. If all three are mixed together we see white light.
Objects absorb and reflect light differently. A lemon reflects yellow light, all the other colours are absorbed and so are not seen by our eyes.
How does sound travel using a medium using the particle theory? (2)
The rapid vibrations of particles cause them to knock into other particles, and this repeats until the sound dissipates into heat.
Describe an experiment to show that sound needs a medium. (2)
The Bell Jar Experiment is used to demonstrate that sound needs a medium to travel. Place an electrical bell in the bell jar and pump out the air of the sealed bell jar. Turn on the electric bell. The sound produced by the bell is not audible to our ears. This demonstrates that the sound waves cannot travel through vacuum and it needs a material medium for its propagation.
Which medium does sound travel fastest through and why? (1)
Solid because it’s particles are closest together.
Which is faster, sound or light? (1)
Light.
Define amplitude, frequency and pitch. (3)
Amplitude is loudness, frequency is number of vibrations per second, and pitch is audible frequency.
