What is sound?
Longitudinal waves caused by vibrations
What is the frequency of sound able to be heard by Humans?
What is the relationship between Frequency and Pitch?
Pitch increases when Frequency increases
- Frequency is the number of cycles per second
What is the relationship between Amplitude and Loudness?
Loudness increases when Amplitude increases
- Amplitude is the size of the waves
What is Ultrasound?
Sound waves above 20000 Hz i.e. cant be heard by humans.
How is Ultrasound useful?
Used in medicine. Ultrasound partially reflects off internal boundaries. Time taken for reflection is the measure of how far away it is.
How does a Transformer work?
An alternating current in the primary coil produces a changing magnetic field in the iron core, hence introducing an alternating p.d. across the secondary coil.
How is the efficiency of the transformer improved?
The iron core is in layers (laminated), to reduce energy loss.
What is the Motor Effect?
The Force exerted on a wire carrying current, in a magnetic field.
What use can be made with the Motor effect?
Split Ring Commutator
How can the Motor effect be changed?
Changes direction if: -current is reversed -magnetic field is reversed
What is the generator Effect?
Potential Difference induced in a wire as it cuts through magnetic field but must be perpendicular.
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What use is made of the generator effect?
Slip Ring Commutator
- Changes direction every half turn
Other examples of Electromagnetic Induction?
- deflection of ammeter pointer as a wire moves in a magnetic field
The Solar System
Why have stars a long time of stability?
Due to Gravity and Radiation pressure.
And because Hydrogen fusion continues until Hydrogen runs out.
What is the life cycle of stars?
Low mass star: Nebula, Protostar, Main stage, Red Giant, White Dwarf, Black Dwarf
High Mass star: Nebula, Protostar, Main Stage, Red Supergiant, White Dwarf, Supernova, Black Hole
Mirrors and Lenses
What sort of images do Convex and Concave Mirrors produce?
Convex: Always Virtual (conVex = virtual)
- Virtual if object is between mirror and principal focus
- Real if object is beyond principal focus
What are Virtual and Real Images?
Real = converge. Rays are brought to a focus.
Virtual = diverge. Image produced is upright and behind the mirror or lens.