Sometimes it is necessary to find a charge of any body on the basis of its interaction with electric field or other bodies in tasks in physics. In most cases neglect the sizes of the body not to count distribution of elementary charges on its weight or a surface.
Instruction
1. For example, how to find charge of a mote weighing 1 mg which flew in uniform electric field tension of 100 sq.m flew by 4 cm and at the same time its speed increased from 1 m/s to 3 m/s?
2. Make short record of conditions of an objective: m=1 of mg, V1=1 m/s, V2=3 m/s, S=4sm, E= of sq.m, q-?
3. Equate force reporting to a mote acceleration to force operating on a mote from uniform electric field. From this equality algebraically express a mote charge: it turns out that the work of mass of a mote and acceleration of a mote is equal to the work of electric field strength and a charge; as a result the charge of a mote is as the relation of the work of mass of a mote and acceleration to the size of electric field strength.
4. Write down the kinematic equation for definition of acceleration of a mote: acceleration is defined as the attitude of a difference of squares of final and initial speed towards the doubled value of the way passed by a mote.
5. Substitute this equation in expression for definition of a charge of a mote. The charge of a mote is equal in a final version to the relation of the work of mass of a mote and the difference of squares of final and initial speeds to the doubled work of the passable way and electric field strength.
6. Check dimension of required size: for this purpose in a final formula for definition of a charge instead of the letters designating physical quantities substitute units of physical quantities expressed in the SI system: the unit of measure of a charge will be defined as the relation of the work of kg • (m/s) 2 to the work of m • In oil; reduce identical units of measure in this fraction; use determination of the physical quantities of 1 Newton and 1 Joule and replace with them certain combinations of physical quantities.
7. Having substituted numerical values, calculate a mote charge. q=10 nkl will turn out