EVERYTHING YOU NEED TO KNOW FOR UNIT 1

the book waffles too much.... heres what you need to know!

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Unit 1
What is inside an atom?
A positively charged nucleus composed of protons and neutrons
Electrons that surround the nucleus
What are isotopes?
Isotopes are atoms with the same number of protons and different numbers of electrons
How do we represent different atoms?
What is specific charge?
The specific charge of a particle is defined as its charge divided by its mass
What keeps protons and neutrons in a nucleus together?
A stable isotope has nuclei that do not disintegrate, so there muse be a force holding them together. We call this force the strong nuclear force because it overcomes the
electrostatic force of repulsion between the protons in the nucleus and (except in unstable nuclei) keeps the protons and neutrons together.
Why are some nuclei stable and others unstable?
Whether nuclei are stable or unstable depend on their neutron:proton ratio.
What happens when an unstable nucleus emits an alpha or beta minus particle?
Alpha radiation consists of alpha particles which each
comprise of 2 protons and 2 neutrons.
Beta radiation consists of fast moving electrons. A beta minus particle is emitted because a neutron is changing into a proton.
What is a photon?
A photon is a `packet' of quantum of electromagnetic waves. An electromagnetic wave consists of an electric wave and a magnetic wave which travel together and vibrate: *at right
angles to each other and to the direction in which they are travelling. *in phase with each other. As you can see the two waves reach peak together so they are in step. When
waves do this we say they are `in phase'.
What is the energy of a photon?
Photon energy E=hf
How many photons does a light source emit every second?
A laser beam consists of photons of the same frequency. The power of a laser beam is the energy per second transferred by the photons. For a beam consisting of photons of
frequency f, the power of the beam=nhf where n is the number of photons in the beam passing a fixed point each second.

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What is antimatter?
Antimatter is antiparticles that each have the same rest mass and, if charged, have equal and opposite charge to the corresponding particle.
What happens when a particle and an antiparticle meet?
When they meet, antimatter and matter particles destroy each other and radiation is released; this is called annihilation. 2 photons are produced in this process. The minimum
energy of each photon produced is hfmin =E0.…read more

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Neutrinos and antineutrinos produced in beta decays are different from those produced by muon decays.…read more

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What is a quantum?
A quantity of energy proportional in magnitude to the frequency of the radiation it represents.
Why can't an electron absorb several photons to escape from a metal?
When light is incident on a metal surface, an electron at the surface absorbs a single photon from the incident light and therefore gains energy equal to hf, where hf is the energy
of a light photon.…read more

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h . The de Broglie wavelength of a particle can be altered by changing the velocity of the particle.
A particle of mass m moving at velocity v has a de Broglie wavelength given by = mv
The velocity of an emitted photon cannot be altered, thus the wavelength cannot be changed.
What is an electric current?
Electric current is the rate of flow of charge in the wire or component.…read more

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resistance increases as it becomes
hotter
What are the characteristics of a diode?
A silicone diode conducts easily
in its `forward direction' above
a Pd of about 0.6v and hardly
at all below 0.6v or in the opposite
direction
What can we use a thermistor for?
A thermistor at constant
temperature gives a straight
line. The higher the temperature,
the greater the gradient of the
line, as the resistance falls with
increase of temperature.…read more

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force due to the pd across the material accelerates until it collides with another positive ion. If a component is at constant temperature, heat transfer to the surroundings takes place
at the same rate. Therefore, the rate of heat transfer=I2R. if the component heats up, its temperature rise depends on the power supplied to it (I2R) and the rate of heat transfer to
the surroundings.…read more

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How can we supply a variable Pd from a battery?
The source pd is connected to a fixed length of uniform resistance wire. A sliding contact on the wire can then be moved along the wire, giving variable pd between the contact and
one end of the wire. A uniform track of a suitable material may be used instead of resistance wire.…read more

Comments

Miss Meera J

Books don't waffle

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