Switch Mode Transformer

Switch mode transformers do not contain an iron core, in order for them to be lighter than traditional transformers. However, since a transformer without an iron core is not as powerful as one with an iron core, switch mode transformers work at a much higher frequency than traditional transformers i.e. the magnetic field changes more often!

Switch Mode:

• more expensive (because more sophisticated technology)
• lightweight (because no iron core)
• more efficient (e.g. for a charger: once the device is fully charged, the transformer won’t take any more current…saves energy…reduces HH energy costs!)*

*ANALOGY: a switch mode transformer is like a can of soda…the current is like the soda inside…charging a phone/device is like pouring the soda out…when the can has been emptied (when the phone is fully charged), no more liquid flows out (no more current passes)

Traditional: (opposite)

• less expensive
• heavier

Transformers: 3 Main Steps

1. Changing magnetic field produced in primary coil by a.c. supply

2. Linked by the magnetic core to the secondary coil

3. This changing field causes an alternating voltage to be induced in the secondary coil

Increasing Accuracy, Reliability and Precision

Accuracy – How close a measurement is to the TRUE value

to increase accuracy, e.g. RE-ZERO a scale, read from a horizontal distance (avoid PARALLAX, position object at ZERO OF A RULER

Reliability – Repetitions

Precision – Decimal Places

Electromagnetic Waves Hazards and Safety Precautions

	Hazard	Safety Precaution
Microwaves	heating of tissue / perceived risk of cancer	close oven door / hands-free cell phone / monitor
Radio
Infrared	risk of skin burning / cell damage	avoid hot places / reflective clothing / avoid exposure (to sun)
Visible light	eye damage	sun glasses / avoid exposure (to sun)
Ultraviolet	risk of {skin / eye} damage / blindness IGNORE: sunburn	skin cream / sunglasses / avoid exposure (to sun)
X-rays	internal heating of body tissue / risk of cancer / cell damage	(lead) shielding / monitor exposure e.g. film badge
Gamma	risk of cancer / cell damage	(lead) shielding / monitor exposure e.g. film badge

 

Great X-tra Ugly Virgins Interest Men Rarely

Radio waves – broadcasting, communications

Microwaves – cooking, satellite transmissions

Infrared – heating, night vision equipment

Visible – optical fibres, photography

Ultraviolet – detecting forged banknotes, fluorescent lamps

X-rays – observing the internal structure of objects/materials

Gamma rays – sterilizing food/medical equipment

Waves

1) Waves transfer energy from one point to another without transferring matter

In transverse waves (e.g. water waves, all electromagnetic waves), the vibrations of the particles are perpendicular to the wave direction 

• crests
• troughs
• wavelength = distance between two successive crests/troughs
• amplitude = vertical distance between the crest/trough and the “middle”
• light waves travel slower in a denser medium

In longitudinal waves (e.g. sound waves), the vibrations of the particles are in the same direction as the wave

• compressions
• rarefactions
• wavelength = distance between two successive compressions/rarefactions
• amplitude = vertical distance between the “top” of the wave and the “middle”
• sound waves travel faster in a denser medium

2) Refraction (the more complicated ones)

Convex lens

White light through a glass prism

Refractive Index of Light 

• Speed of light in air ÷ speed of light in medium
• Refractive index for glass is 1.5, for water is 1.33 (means that light will be bent more in glass than in water)

3) Critical Angles and Total Internal Reflection

• angle of incidence = critical angle… light travels along surface of medium
• angle of incidence > critical angle = light is reflected back into the denser medium

Optical Fibres

• made of glass
• used in telecommunications (transmit data/voice/images, as light signals, over long distances)
• used in medicine

Advantages: 

• cheaper than copper wires
• thinner than copper wires (more fibres per cable diameter so more information transmitted)
• clearer signal (electrical signals in copper wires interfere with other copper wires in the same bundle – optical fibres carry light signals so no interference among cables in a bundle)
• signals travel much farther than in copper signals, with the same amount of power

4) Diffraction

5) Sound waves: no medium, no sound

• In air, disturbances are passed from air molecule to air molecule
• In a vacuum, there is no medium to carry the disturbances produced by the vibrating object

6) Musical notes

• Higher frequency = higher pitch
• Higher amplitude = higher volume i.e. louder
• Quality/timbre depends on waveform

Experiment to Measure the Speed of Sound in Air

1. Stand a measured distance from a building with a large, flat wall. Try to have no obstacles in the way.
2. As a trial, clap two wooden blocks together. An echo is heard: this is the clapping sound traveling to the wall and reflecting back at you. Clap repeatedly in time with the echoes (clap – echo – clap – echo etc.). Once a constant rhythm is achieved…
3. Have someone begin timing as you clap 51 times, stopping time on the 51st clap.
4. To calculate the speed of sound, divide 2x the distance to the wall by 1/50th the time for the 50 claps (the 51st is not included because that is when the stopwatch stopped timing).