lesson 6 - lenses #2

OpticsHD by Andrew Duffy

https://appsto.re/gb/0F16O.i

that's it

practise drawing ray diagrams !!

lesson 5 - lenses#1

first of all - the stuff about light from year 9

the new stuff relies on you understanding the physics from P1 - please get back to me with questions about that

Lenses rely on a good understanding of REFRACTION - so - here goes 

REFRACTION HAPPENS WHEN LIGHT CHANGES SPEED AT A BOUNDARY

the best diagram in the world shows this 

Light is refracted through a glass block like this :

can you compare the car diagram with the glass block diagram?

the angles involved in REFRACTION are governed by SNELL'S LAW

- the refactive index (n) is a constant that is a property of transparent materials

n = sin i / sin r

if glass blocks are shaped in a certain way, they will bring light to a focus - the shape is called CONVEX and the distance between the middle of the lens and the focal point is called the FOCAL LENGTH (you can find this number on the side of camera lenses)

Convex lenses can be used as cameras, projectors or magnifying glasses - the first two produce images that are REAL (an image that forms on a screen) but a magnifying glass forms an image that is VIRTUAL (that needs to be seen by someone's eyes).

we will learn how to construct these diagrams next lesson

lesson 4 - ultrasound

sound travels through solids more quickly than through solids

sound travels through liquids more quickly than through gases

humans have a hearing range of 20Hz to 20kHz (this range diminishes with age)

sound with a frequency of greater than 20kHz is called ULTRASOUND

Amplitude - loudness

Wavelength - length of wave

Frequency - waves per second - 1/time period

use of ultrasound #1 - medical scanning

an ultrasound probe emits ultrasound waves and listens for their echoes

the computer that the probe is connected to does millions of distance = speed x time calculations

in order to work out where the baby is positioned

the computer draws a picture of the baby (either as a 2D or a 3D image)

use of ultrasound #2 - cleaning delicate items

sound can make objects resonate - this happens if a forcing signal has a frequency that matches the natural frequency of the object 

if jewellery is placed in an ultrasonic cleaner, the dirt particles are literally shaken off the jewellery by the vibrations of the ultrasound

use of ultrasound #3 - destroying kidney stones

even kidney stones have a natural frequency

an ultrasonic probe can be used to vibrate stones at their natural frequency causing then to shatter

they then pass out of the body via the bladder instead of needing surgery

lesson 3 - moments

clockwise moments = anti-clockwise moments

moment = force x distance

how does this balance ?

lesson 2 - centre of mass

just a video

https://m.youtube.com/watch?v=qRsJXXb9WNE

you need to be able to describe how to find the centre of mass in regular and irregular objects

you need to be able to say why some objects are more stable than others (base area, position of CoM)

exam dates

B2 and B3 - 12 May 2015

C2 and C3 - 14 May 2015

P2 and P3 - 20 May 2015

B1 - 5 June 2015

C1 - 9 June 2015

P1 - 12 June 2015

lesson 1 - X-rays

just a video

https://m.youtube.com/watch?v=8pBjobqdtrc

plus remember this list

RADIO

MICRO

INFRA-RED

VISIBLE

ULTRA-VIOLET

X-RAY

GAMMA

as you go down the list - 

their wavelength decreases, their frequency increases and their danger increases

questions that you should be able to answer :

how do you get a picture of bones using x-rays? (shadows, absorb, transmit)

what are x-rays used for? (diagnosis, treatment)

how do medics keep themselves safe? (screen, lead, leaving the room)

and - here is an X-ray photo of my head - July 20th 1969