What are the physical quantities defined by the ratio definition method

1. Density. The density of p at any point in the object is defined as = m v, where v is the volume element containing p points. m is the mass of the volume element. In centimeter-gram-second, the unit of density is g cm; International System of Units and Chinese Legal Units of Measurement.

, the unit of density is kg m.

2. Speed. The formula for calculating velocity is v=δx δt. The unit of velocity in the SI system of units is meters per second. The velocity is numerically equal to the ratio of the displacement of the object's motion to the time it takes for that displacement to occur.

The common units of speed are: centimeter seconds, meter seconds, kilometers and hours. The magnitude of velocity is also called velocity.

3. Power. Power refers to the amount of work done by an object per unit of time, i.e., power is a physical quantity that describes how fast or slow work is done.

The formula for power is power = work time. Power is a physical quantity that characterizes the degree of work done fast or slow. The work done per unit of time is called power and is denoted by p.

4. Pressure. The ratio of the pressure to the area of force on an object is called pressure, and pressure is used to compare the effect of pressure, the greater the pressure, the effect of pressure.

The more obvious. The formula for calculating the pressure is: p=f s, and the unit of pressure is pascal.

Abbreviated as Pa), the symbol is Pa.

5. Electric field strength.

Field strength is the electrostatic force experienced by a charge placed at a point in an electric field.

f and the amount of charge it has.

Ratio, defined by e=f q, applies to all electric fields; where f is the force of the electric field on the test charge, and q is the amount of charge of the test charge. Unit n c.

The ratio method is to apply the ratio of two physical quantities to quantitatively study the third physical quantity. It applies to the definition of properties or characteristics of matter, characteristics of the motion of objects.

The application of the ratio method to define physical quantities often requires certain conditions. The first is that it is objectively necessary, the second is that the two physical quantities that indirectly reflect the characteristic properties can be measured, and the third is that the ratio of the two physical quantities must be a fixed value.

For example: velocity, acceleration, density, specific heat capacity, resistance, capacitance, electric field strength, magnetic induction strength, etc.

Senior 3 Physics Special Topics Review the Physical Quantities of the Ratio Definition Method.

Junior high: density, =m v

Power, p=w t

Velocity, v=s t

pressure, p=f s

High School: Acceleration, a=(δv) (t).

Linear velocity, v=(δl) (t).

angular velocity, =t).

Induced EMF cautious, e=(δt).

Electric field strength, e=f q

Capacitance, c=q u

resistance, r=u i

Magnetic induction strong wide stool Qi absolute, b=f (il).

For example, velocity v=s t e=f q e=u d, etc. are all defined by the ratio method.

Acceleration, average power, efficiency, electric field strength, magnetic induction strength, electric potential, current intensity (i=q t), and so on.

The electric field strength is definitely defined by the ratio method, which is defined by e f q

The --- of physical quantities defined by the ratio definition method

Junior high: density, =m v

Power, p=w t

Velocity, v=s t

pressure, p=f s

High School: Acceleration, a=(δv) (t).

Linear velocity, v=(δl) (t).

angular velocity, =t).

Induced electromotive force, e=(δt).

Electric field strength, e=f q

Capacitance, c=q u

resistance, r=u i

Magnetic induction intensity, b=f (il).

Ratio definition method, that is, when defining a physical quantity judge, the form of ratio is defined, for example: density is defined as the ratio of slippery mass to volume, i.e. = m v; Velocity is defined as the ratio of displacement to time, i.e., v = δx δt; Acceleration is defined as the ratio equal to the amount of change in velocity to time, i.e., a=δv δt.

A test question analysis: the so-called ratio definition method is a method to define a new physical quantity with the "ratio" of two basic physical quantities The basic feature of the definition of the ratio method is that the defined physical quantities often reflect the most essential properties of matter, and it does not change with the size of the physical quantities used in the definition.

a. Induced electromotive force and <>

proportional, so <>

It does not belong to the ratio definition method; That's right.

b. Capacitance c is determined by the nature of the capacitor itself, and has nothing to do with the amount of charge and the potential difference between the two plates, so it is <>

It belongs to the ratio definition method; Mistake.

c. The resistance is determined by the nature of the conductor itself, and has nothing to do with the voltage at both ends of the conductor and the current through the conductor, so it <>

It belongs to the ratio definition method; Mistake.

d. The intensity of magnetic induction has nothing to do with the current element put into the magnetic field, so it <>

It belongs to the ratio definition method; Mistake.

Therefore, choose a comment: understand the characteristics of the ratio definition method: the physical quantity to be defined is often the most essential property of the matter, and it does not change with the size of the physical quantity used in the definition.

a. The resistance of the conductor r= l

The resistance in S is related to the length, cross-sectional area and resistivity of the wire, which does not belong to the ratio definition method, so A is wrong;

b. The acceleration of a depends on the magnitude of the force, which does not belong to the ratio definition method, so b is wrong;

c. The electric field strength e of the point charge depends on the electric charge and distance, and is related to the electric amount; It does not belong to the ratio definition method, so c is wrong;

d. In the definition of capacitance, C has nothing to do with the amount of electricity between the two plates and the potential difference between the two plates, and belongs to the ratio definition method, so D is correct;

Therefore, d

a. Acceleration a is proportional to the resultant force and inversely proportional to mass, not a ratio definition method so a is wrong

b. Magnetic induction intensity b=f

qv is not a ratio definition, but b=f

The magnitude of il, b and f has nothing to do with the magnitude of il, it is a ratio definition method Therefore b is wrong C, the electric field strength e is related to the amount of charge q of the field source, so E=kqr is not a ratio definition method Therefore c is wrong

d. The resistance r is not directly related to the voltage and current, and the resistance r=ui is defined by the ratio method, so d is correct

Therefore, d