IAL phy U2 caqs/PP mistakes

B is correct answer

constructive interference:
path diff = nλ (where n = whole number)

phase difference = 2n(π)


destructive interference:
Path difference = (n +1/2)λ

phase diff = (2n+1)π


NOTE: for phase difference, we need even INTEGER multiples of π,
so phase diff of 0.5π, 3.5π etc give neither constructive nor destructive interference, thats why C is wrong.
(they give partial interference)

define polarised light

polarised light is when light is restricted so it has oscillations in a single direction which is perpendicular to direction of wave travel

OR in terms of plane:
“ “so it oscillates in a single plane which includes direction of wave travel

NOTE:
say the blue part/plane was flitered, it still wudnt be right to say perpendicular when talking about plane, as the oscilation includes the direction of wave travel

if you talk about the blue and red lines(wave directions), then yes the blue/red wave is perpendicular too direction of wave travel

C is correct answer

in diffraction grating experiment:
-diffraction grating is set upparallel to screen
- diffraction grating is setup perpendicular to light source

- diffraction grating is the square thingy with 1000s of line holes or slits

- - we find theta using trigonometry NOT PROTRACTOR
- distance between the bright dots(maxima) is best measured using a metre rule

in series, voltage is shared so if V2 increases v1 must decrease to yk balance out the ratios of share

Explain how the ultrasound scan of the unborn baby is produced using pulse-echo technique (6marks)

• a device/transdurcer is used that produces ultrasound and also detects the ultrasound reflected back

• the produced ultrasound is the pulse which is reflected when it hits a boundary, and the reflected ultrasound is the echo

• they get reflected due to change in density (like from body fluid to soft tissue)

• speed of ultrasound is known and the time taken for pulse to return is measured

• the distance from transducer to boundary is found with equation:

s = v x t, but here its 2d = v x t, therefore distance = (vxt) / 2
(the distance is found to create an accurate mapping of the image)

• the echoes are converted to electrical signanls and computer uses the echo intensity and time delays to display as an ultrasound scan/image

btw reflected due to change in denisty is cuz of acoustic impedence,a quantity determines how much sound waves are resisted to flow past a medium. but this is not in syllabus so you can ignore it

define work function

minimum energy required to emitt/remove an electron from the surface of a metal

In an experiment involving photocell, the intensity of UV light emitted was increased.
Explain what happened to the reading on ammeter (3marks)

• increasing intensity means more photons hit metal surface per second
  
  

• so more electrons(photoelectrons) are emitted per second
  
  

• therefore current increases (or reading on ammeter increases)

(as rate of flow of charge increased)

Explain, using Huygens' construction, how diffraction occurs as waves pass through a gap.

[2marks]

• in Hyugen's construction, points along the wavefront (called point sources) acts as a source for secondary waves/wavelets
  
  

• so when waves pass slit they bend and spread out (diffraction)

here you should have figured out that there are sever maximums or maximas, central one being largest and others smaller

these maxima are due to (constructive) interference between the secondary wavelets
dark patches due to destructive interference

define emf

define potential difference

emf = energy supplied per unit charge by a source

p.d = energy transferred per unit charge between two points in a cicuit

• Plot a graph V(y-axis) against I (x-axis)
  
  

• Determine the gradient from graph
  
  

• Gradient is −r, so r is - gradient

The calculated value for resistivity of air in lightning channel is 0.2 and accepted value is 10¹⁶

Suggest why the value calculated from the data is so much less than the accepted value.

Lightning channel unlikely to have a uniform diameter / CSA
(cuz lightning is non uniform)