By controlling how often the rapid pulses of radar energy are sent out by a radar transmitter (called the transmitter's "pulse timing"), and how long it takes for the reflected pulse energy to come back to the radar receiver, one can tell not only where objects are, but also how far away they are. Digital circuits in a radar receiver calculate the distance to an object by knowing the time interval between energy pulses. The radar receiver's digital circuits count how long it takes between pulses for an object's reflected energy to be detected by the radar receiver. Since radar pulses are sent and received at approximately the speed of light, the distance to an object can easily be calculated. This is done in digital circuits by multiplying the speed of light by the time it takes to receive the radar energy reflected back from an object.
The time between pulses (often called "pulse rate time", or PRT) sets the limit on how far away an object can be detected. That distance is called the "range" of a radar transmitter and receiver. Radar transmitters and receivers use long PRT's to find the distance to objects that are far away. Long PRT's makes it possible to accurately determine the distance to the moon, for example. Fast PRT's are used to detect objects that are much closer, like ships at sea, high flying aircraft, or to determine the speed of fast moving automobiles on highways.
Digital circuits are used for signals that only turn on and off instead of often working at levels somewhere between on and off. Active components in digital circuits typically have one signal level when turned on, and another signal level when turned off. In general, in digital circuits a component is only switched on and off.
Computers and electronic clocks are examples of electronic devices that are made up of mostly digital circuits.
Basic blocks:
Complex devices:
Scalar
Scalars are simple numbers. They are used for measuring things. Many things can be measured, and the measure can be explained by only giving the number.
Suppose we are measuring a rod. We could give the measured length as 2 metres or 3 cm—depending on the length of the rod under observation. Here, only the figure 2 or 3 along with the unit of measure is enough to transmit information about the rod.
Other examples of scalars are:
In other words, mass is measured by scalars, just like distances are measured by scalars.
In mathematics, scalars are distinguished from more complex mathematical objects such as vectors and matrices in that they consist of only one number. A scalar formula_1 can also be multiplied to a vector formula_2 or a matrix formula_3, resulting in the vector formula_4 and the matrix formula_5, respectively. For vectors, scalar multiplication produces a new vector of different length in the same or opposite direction of the original vector.
Photon
Photons (from Greek φως, meaning "light"), in many atomic models in physics, are particles which transmit light. In other words, light is carried over space by photons. Photon is an elementary particle that is its own antiparticle. In quantum mechanics each photon has a characteristic quantum of energy that depends on frequency: A photon associated with light at a higher frequency will have more energy (and be associated with light at a shorter wavelength).
Photons have a rest mass of 0 (zero). However, Einstein's theory of relativity says that they do have a certain amount of momentum. Before the photon got its name, Einstein revived the proposal that light is separate pieces of energy (particles). These particles came to be known as photons.
A photon is usually given the symbol γ (gamma),
Photons are fundamental particles. Although they can be created and destroyed, their lifetime is infinite.
In a vacuum, all photons move at the speed of light, c, which is equal to 299,792,458 meters (approximately 300,000 kilometers) per second.
A photon has a given frequency, which determines its color. Radio technology makes great use of frequency. Beyond the visible range, frequency is less discussed, for example it is little used in distinguishing between X-Ray photons and infrared. Frequency is equivalent to the quantum energy of the photon, as related by the Planck constant equation,
where formula_2 is the photon's energy, formula_3 is the Plank constant, and formula_4 is the frequency of the light associated with the photon. This frequency, formula_4, is typically measured in cycles per second, or equivalently, in Hz. The quantum energy of different photons is often used in cameras, and other machines that use visible and higher than visible radiation. This because these photons are energetic enough to ionize atoms.
Another property of a photon is its wavelength. The frequency formula_4, wavelength , and speed of light formula_7 are related by the equation,
where formula_9 (lambda) is the wavelength, or length of the wave (typically measured in meters.)
Another important property of a photon is its polarity. If you saw a giant photon coming straight at you, it could appear as a swath whipping vertically, horizontally, or somewhere in between. Polarized sunglasses stop photons swinging up and down from passing. This is how they reduce glare as light bouncing off of surfaces tend to fly that way. Liquid crystal displays also use polarity to control which light passes through. Some animals can see light polarization.
Finally, a photon has a property called spin. Spin is related to light's circular polarization.
Light is often created or absorbed when an electron gains or loses energy. This energy can be in the form of heat, kinetic energy, or other form. For example, an incandescent light bulb uses heat. The increase of energy can push an electron up one level in a shell called a "valence". This makes it unstable, and like everything, it wants to be in the lowest energy state. (If being in the lowest energy state is confusing, pick up a pencil and drop it. Once on the ground, the pencil will be in a lower energy state). When the electron drops back down to a lower energy state, it needs to release the energy that hit it, and it must obey the conservation of energy (energy can neither be created nor destroyed). Electrons release this energy as photons, and at higher intensities, this photon can be seen as visible light.
In particle physics, photons are responsible for electromagnetic force. Electromagnetism is an idea that combines electricity with magnetism. One common way that we experience electromagnetism in our daily lives is light, which is caused by electromagnetism. Electromagnetism is also responsible for charge, which is the reason that you can not push your hand through a table. Since photons are the force-carrying particle of electromagnetism, they are also gauge bosons. Some matter–called dark matter–is not believed to be affected by electromagnetism. This would mean that dark matter does not have a charge, and does not give off light.
Vector
A vector is a mathematical object that has a size, called the "magnitude", and a direction. It is often represented by boldface letters (such as formula_1, formula_2, formula_3), or as a line segment from one point to another (as in formula_4).
For example, a vector would be used to show the distance and direction something moved in. When asking for directions, if one says "Walk one kilometer towards the North", that would be a vector, but if they say "Walk one kilometer", without showing a direction, then that would be a scalar.
We usually draw vectors as arrows. The length of the arrow is proportional to the vector's magnitude. The direction in which the arrow points to is the vector's direction.
The Head to Tail method of adding vectors is useful for doing an estimate on paper of the result of adding two vectors. To do it:
It's called the "Head to Tail" method, because each head from the previous vector leads in to the tail of the next one.