Transmission

Question 1

how do longitudinal waves progress

Answer 1

by the interaction of particles oscillating along the direction of travel of the waves

Question 2

what is the estimated value of sound in air

Answer 2

340ms-1 at 20C

Question 3

how does the speed of sound change if it were travelling through a solid

Answer 3

• it would be much faster
• due to the strong bonds between the particles in a solid and the fact that their closer together
• allowing for the energy to be transmitted more effectively and quickly

Question 4

a model of masses connected by springs shows how particles moving sideways enables a wave to progress perpendicularly to the oscillation. The distance between the masses at rest due to the springs is x, while the distance between two masses where one is in motion is x + delta x (due to the extension of the spring). For the mass in motion connected to the mass at rest and that mass at rest connected to the next mass at rest, how would you represent x, the distances, with forces

Answer 4

• the x could be labelled as T, tension
• while the delta x could be labelled as delta F, change in force
• meaning between the two resting balls there is just T
• and between the ball in motion and the first resting ball there is T + delta F due to increased tension

Question 5

the force T is in the horizontal direction to the right. The direction of T + delta F is past 90 degress of T, pointing in the north-west direction. What would be the equation to work out the vertical component of tension and why

Answer 5

• you would need to draw a vertical line in between the horizontal T and the T + delta F
• the angle between the T + delta F and the ‘normal’ to T is theta
• this makes T + delta F the hypotenuse, and the vertical component the adjacent
• so you use cos (CAH) to get cos theta = A / T + delta F
• leaving you with the equation for the vertical component being cos theta x (T + delta F)

Question 6

what would be the equation to work out the vertical component of the extra tension, using the previous equation

Answer 6

delta F x cos theta

Question 7

how does this then relate to how the particles moving sideways causes the wave to progress

Answer 7

• the stationary particle will be pulled upwards by the particle (mass) in motion due to the vertical component of the extra tension (delta F x cos theta)
• only the vertical component is used because we only care about the movement upwards and downwards

Question 8

what does the speed that the pulse moves along the row of masses depend on

Answer 8

• the magnitude of the masses

- the tension of the springs

Question 9

what is the equation for the speed of a transverse wave moving along a stretched wire

Answer 9

• c = the root of (T / u)
• where T = the tension in the wire
• and u (greek letter mu) = the mass per unit length

Question 10

what makes water waves more complex than waves moving along stretched wires

Answer 10

• particles near the surface of the water rotate so the up and down motion of the surface progresses
• the speed of the surface wave also depends on the elastic properties and mass of the particles
• as well as the depth of the liquid

Question 11

what is the speed of an electromagnetic wave in a vacuum

Answer 11

3x10^8 ms-1

Question 12

what is the speed of light passing through something dependent on

Answer 12

the atomic structure of the medium

Question 13

why do we see colours in general

Answer 13

• because some materials reflect or absorb a range of wavelengths but transmit others
• such as an apple looking red because it absorbs all other wavelengths of light
• but reflects the wavelength of light corresponding the red end of the visible spectrum

Question 14

what is the intensity of radiation known as

Answer 14

the power per unit area of the radiation falling on to a surface

Question 15

what is the equation for intensity

Answer 15

• intensity = power / area

- I = P / A (Wm-2)

Question 16

what is intensity also referred to as

Answer 16

radiant flux