To better understand the relationship between different parameters, we can condense all the equations used to find voltage, current, resistance, and power into a simple pie chart of Ohm`s law, as shown below. where we used the definition of current density and also defined σ = n e e 2 ν m e {displaystyle sigma ={n_{e}e^{2} over nu m_{e}}} which is the electrical conductivity. This equation can also be written equivalently, because resistors are one of the most important blocks of electrical circuits. They consist of the mixture of clay or carbon and are therefore not only good conductors, but also good insulators. Most resistors have four color bands. The first and second bands display the first and second digits of the value, respectively. The third band is used to multiply the value digits and the fourth band gives us tolerance. If there is no fourth band, the tolerance is assumed to be plus or minus 20%. where J is the current density in I/(m·m) or I/g, depending on how the systems are compared, I is the current (A), A is the cross-section (m·m) and m is the mass (g). Note that j is often used for electricity instead of I to avoid confusion with imaginary numbers.
Therefore, attention should be paid to the definitions of symbols, as they can vary from case to case. 3) A magnetic field is aligned at an angle of 47° to the normality of a rectangular area of 5.1 cm x 6.8 cm. If the magnetic flux through this surface is 4.8 x 10-5 T·m2, how strong is the magnetic field? Φ = BA cosθ 4.8 x 10-5 = B (0.051 * 0.068) cos(47°) B = 0.02 T In circuit analysis, three equivalent expressions of Ohm`s law are used interchangeably: Ohm`s law can be used to validate static values of circuit components, current levels, power supplies, and voltage drops. For example, if a tester detects a higher than normal current reading, it may mean that the resistance has decreased or the voltage has increased, resulting in a high voltage situation. This may indicate a power or circuit problem. (11) Two cylindrical wires are made of the same material and have the same length. If wire B is to be nine times the resistance of wire A, what should be the ratio of its rays rB/rA? RA = ρL / πrA2 and RB = ρL / πrB2 So if you assimilate and solve them for rB/rA, the ratio is 1/3. Voltage is the most commonly used term for the difference in electric potential between two points and provides the “thrust” that allows electric charge to move around a conductive loop. (36) A 0.76 m long metal rod moves at a speed of 2.0 m/s perpendicular to a magnetic field.
If the EMF induced between the ends of the rod is 0.45 V, how strong is the magnetic field? = Bvl 0,45 = B (2) (0,76) B = 0,296 T The resistance is the resistance to the movement of the load. The resistance is similar to the effects of friction in flowing water or a slippery object. The units of resistance are the ohms, denoted by the capital letter omega. To calculate the amount of resistance in an object, the following equation can be used: The law of ohms is used in any electrical device to apply the correct amount of charge to a given resistance. While doctors don`t need to easily calculate the voltage, current, and resistance of these devices, understanding the relationship can provide insight into how electrical devices work. Ohm`s law is also present in the human body and has several applications. For example, nerves in the nervous system use electrical properties to relay messages to each other. These electrical signals can be imaged with sensors and better understood by doctors. Gao et al.
and Su et al. studied the electrical properties of bones and advanced the treatment of bone diseases. The human body contains many electrical pathways and processes. By understanding the basic equation, clinicians can work to solve problems in new ways. You can use the magic triangle of Ohm`s law to remember the different equations of Ohm`s law used to solve various variables (V, I, R). If the value of the voltage is queried and the values of the current and resistance are given, then to calculate the voltage, it is enough to cover V above. That leaves the I and R or I × R. The voltage equation is therefore the current multiplied by the resistance. Examples of how the magic triangle is used to determine voltage using Ohm`s law are listed below. A hydraulic analogy is sometimes used to describe Ohm`s law. Water pressure, measured by Pascal (or PSI), is the analogue of voltage, because the creation of a difference in water pressure between two points along a (horizontal) pipe causes water to flow. The flow of water, as in liters per second, is the analogue of current, as in coulombs per second.
After all, flow limiters – such as openings in pipes between points where water pressure is measured – are the analogue of resistors. We say that the flow of water through an orifice limiter is proportional to the difference in water pressure through the reflector. Similarly, the flow rate of the electric charge, i.e. the electric current, through the electrical resistance is proportional to the voltage difference measured through the resistance. The main problem with Ohm`s law is that calculations can become complex with advanced circuits and electrochemical phenomena. For example, total resistance is composed of different types of resistance, for example ohmic resistance, mass transfer resistance, and charge transfer resistance. When optimizing the electrical performance of devices, there is a trade-off, reducing one resistance can increase another. This is an important consideration in design and optimization studies to determine which values are best for a particular application. Often, these different types of resistance are difficult to measure and require sophisticated machines to provide accurate values. In addition, resistance changes over time as the structural integrity of a device deteriorates. It can also alter the expected results of Ohm`s Law if this is not taken into account. [5] [6] To get a first idea of what is happening, it is possible to compare the electrical situation with that of the flow of water in a pipe.
The voltage is represented by the water pressure of the pipe, the current is represented by the amount of water flowing through the pipe, and finally the resistance is the equivalent of the size of the pipe. 56) The current in an RL circuit rises to 95% of its full scale 2.24 s after the switch is closed. a) What is the time constant for this circuit? (b) If the inductance in the circuit is 0.275 H, what is the resistance? (a) I (t) = ( / R) (1 – e-t/τ) 0.95 I = ( / R) (1 – e-t/τ) 0.95 ( / R) = ( / R) (1 – e-t/τ) 0.95 = 1 – e-t/τ -0.05 = -e-t/τ ln(0.05) = -T / τ τ = 0.75 S Ohm`s law was originally an empirical derivative based on the relationship between current and voltage; However, it remained consistent in microscopic and macroscopic observations.
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