Waves

• Wavelength is the distance between 2 consecutive creasts, measured in m
• Frequency is the number of crests that pass through a given point per second, measured in Hz or s in -1
• Velocity is the distance a wave travels through space per unit of time, measured in m/s
• Frequency = velocity / wavelength
• Electromagnetic radiation is the type of energy
• As energy travels forward, electric and magnetic fields are created perpendicular to each other and to the direction of travel
• If electromagentic radiation travels in vaccuum, its velocity is equal to the speed of light, which is 3 x 10 in 8 m/s
• c (speed of light) = frequency x wavelength
• Electromagentic radiation spectrum is written in the order of increasing frequency and decreasing wavelength
• EMR spectrum: infrared, ROYGBIV, ultraviolet, Xray, gamma rays
• To calculate energy of 1 EMR photon, we use Planck's equation
• Plank's equation: E = h x f = h x c / wavelength
• As energy of electromagnetic wave goes up, its frequency should increase or its wavelength should decrease
• de Broglie's postulate describes relationship between wavelength and mass
• As per de Broglie's postulate, wavelength = Planck's constant / momentum = Planck's constant / mass x velocity
• momentum (p) = mass x velocity
• Heisengerg uncertainty principle tells us that the exact position and momentum of electron cannot be measured simultaneously
• Work function (W) is calculated by the same equation as energy of 1 photon, which is E = h x frequency
• Only if frequency of incoming photon is at the threshold frequency, the electron will be emitted
• If the frequency of photon is above the threshold frequency, then the difference is emitted as a kinetic energy
• Kinetic energy (Ek) = E of light - W
• The speed of electron emitted by te photoelectric effect can be calculated as kenetic energy = 1/2 x mass x velocity in square
• To increase kinetic energy, we need to increase the energy of photon
• To increase number of ejected electrons, we need to increase intensity or number of photons
• Fluorescent light (emitted by electron excitation) should be of lower energy or higher wavelength than the light used to cause the excitation