Ohm is the unit of resistor, which is to commemorate students of Ohm .
What is a resistor? R (ReSIstor)
is the hindering effect on current. R=U/I Ohm's law
U=I*R
I=U/R
Resistance: R is ohm
Voltage: U is volts (V)
Current: I is ampere (A)
Voltage: multimeter is used to measure voltage, current, and resistance.
measures two parameters and can calculate the third parameter.
Current I is the basic physical unit.
Ampere's law is the law of magnetic interaction between current and current. It was discovered by Ampere in 1820 and is one of the basic laws of electromagnetics. Its content is: the magnitude of the interaction force between the two element currents is proportional to their current intensity I₁, I₂, and the lengths of the two current elements dL₁ and dL₂, respectively, and is inversely proportional to the square of the distance r₁₂. The direction of the force is both perpendicular to dL₂ and perpendicular to the plane where dL₁ and r₁₂ are located.
In order to commend Ampere's achievements, in 1881, the first International Electrical Conference held in Paris decided to name the current unit with Ampere. How to define
amps? (Units of current) After three definition changes in history
1908, the constant current of 1.11800.02 mg of silver can be electrolyzed from silver nitrate solution within a 1-second interval of 1 ampere, also known as international ampere.
1946, the International Measuring Commission (CIPM) proposed to define it as: in a vacuum, two parallel and infinitely long circular straight wires with negligible cross-sectional area are passed with an equal amount of constant current, and the interaction force between the wires is 2×10-7 knots in a length of 1 meter, the current in each wire is 1 ampere, also known as absolute ampere. This definition was adopted by the 9th International Measuring Conference (CGPM) in 1948.
On November 16, 2018, the 26th International Conference on Measuring passed the resolution "Revised the International System of Units", defining 1 ampere as "the current intensity generated by the movement of (1/1.602176634)×10^19 electrons within 1 s". This definition will officially come into effect on on World Measuring Day on May 20, 2019. How to define
volt ? (Unit of voltage)
consumes 1W of power between two points carrying 1A constant current wire, and the potential difference between these two points is 1V. Volts can also be expressed in the formula: 1V= 1W/A.
voltage unit is volt (volt), referred to as volt for short. In international unit system (SI), the symbol is V, that is, when the electric field force moves 1 Coulomb (C) positive charge from point a to point b is 1 Joule (J), the voltage between points a and b is 1V. How to define
Newton ? (Unit of Force)
Newton is defined as: adding to an object with a mass of 1kg, so that the force that generates an acceleration of 1m/s2 is 1N. Its dimension is [F]=M・L・T-2, that is: 1N=1kg×1m/s2.
N Newton
Jule How to define it? (Unit of energy work)
Joule (referred to as focal, symbol J), is the international unit of energy and work. The work done by moving 1 meter away from the action point of 1 Newton in the direction of the force. How to define
watts? (Units of Power)
is 1 watt for 1 joule per second. The voltage is 1 volt and the power of a constant DC current of 1 am, that is, 1 watt
seconds how to define it? (Units of Time)
seconds (second) is the basic unit of time in the International System of Units, and the symbol is s. Sometimes it is also borrowed in the English abbreviation and marked as sec. Definition of
seconds: When the cesium-133 atom is located at sea level and is in a non-perturbing ground state, the radiation frequency ΔνCs corresponding to transition between the two superfine energy levels is expressed in units of Hz (that is, equal to s-1). When the fixed value is selected 9192631770 times to define the second. How is
meters defined? (Units of length distance)
"meter" definition originated in France.The length of 1 meter was initially defined as one tens of millions of the distance from the Earth's equator to the North Pole of through the meridian of Paris, and was subsequently determined with the International meter original .
Starting from May 20, 2019, the definition of meter is updated to: When the speed of light c in the vacuum is expressed in units of m/s, a fixed value of 299 792 458 is selected to define meter. where seconds are defined by the frequency ΔνCs of cesium. How to define
kilogram? (Units of mass)
1791 stipulates: 1 cubic decimeter of pure water at 4°C, and the raw material is made of platinum-iridium alloy, and stored in Paris, later called international kilogram raw material .
methods use the Watt equilibrium method (also called Watt balance) to define Planck's constant. The scientists' idea is that one end of the watt balance contains a normal balance. At the beginning, the researchers hung an object with a mass of m at one end of the normal balance, and hung a coil with a total length of L at the other end. The coil is located in a magnetic field with a magnetic field strength of and B. When the coil passes a current with intensity i, the coil is subjected to a force of magnitude BLi. Carefully adjust the current intensity until the balance is just balanced (that is, to make mg=BLi), and then you can associate it with the Planck constant through a series of equations. But the reality is not that simple. Scientists still need to measure other values, such as the magnitude of local gravity, the largest source of error, and avoid any form of vibration.
In 2007, Pratt used the Watt balance method to measure the most accurate Planck constant value to date - with the relative uncertainty of 36/109.
Planck constant?
Planck constant is denoted as h, which is a physical constant used to describe the size of quantum . In atomic physics and quantum mechanics , Max Planck studied the law of thermal radiation in 1900 and found that only by assuming that the emission and absorption of electromagnetic wave are not continuous, but are performed one by one, can the calculation results be consistent with the experimental results. Such a part of energy is called energy nubs, and each part of energy nub is equal to the Planck constant multiplied by the frequency of the radiated electromagnetic wave.
During the emission and absorption of light waves, the energy changes of objects are discontinuous, or in other words, objects change their energy discontinuously through separate jumps, and the energy value can only be an integer multiple of a certain minimum energy element. To this end, Planck also introduced a new natural constant h=6.626196×10-34 J·s (i.e. 6.626196×10-27 erg·s, because 1erg=10-7 J). This hypothesis was later called the energy quantization hypothesis, where the smallest energy element is called the energy quantum, and the constant h is called the Planck constant.
