5. Data processing

(Same as in Laboratory work № 2-2).

6. Work execution order and experimental data analysis

1. Mount the scheme (see Fig. 33).

2. Measure the diameter of a coil with help of a ruler (accurately for millimeters) for one time.

3. Draw the exploring part of desktop in a smaller scale into your report. In the middle of a sheet draw a line along its larger side (this line corresponds to midline of desktop, parallel to the laboratory panel). Draw three equidistant lines perpendicular to that line. You’ll have to determine Н_h in the points of intersection of these lines.

4. Set the tangent compass so, that the center of magnetic arrow appears in one of chosen points.

5. Inspect the tangent compass: the origin of of compass scale should coincide with a plane of coils.

6. Place a coil of tangent-compass so, that the plane of its coils coincides with vertical plane, passing through desktop midline (origin of of compass scale correspond with right side of desktop midline). Determine the direction of Н_h. In order to do this, in the absence of a current angle  measures between direction of a needle and the origin of of compass scale (right side of plane of coils). Write its value into the table of measurements.

7. Determine magnitude of Н_h. Place tangent-compass so, that magnetic needle appeares in the plane of coils in the absence of current. The needle should coincide with origin of of compass scale.

8. Turn the current on and using a resistors box R₃ achieve 30⁰ or 45⁰ deviation of a needle from origin position.

9. Write the scale readings of milliamperemeter and compass scale (value of angle α of deviation of a needle from its zero position) into the table of measurements.

10. Calculate the magnitude of Н_h using the formula (95). Number of winds N is written on the label of a coil.

11. Do steps 4 – 9 for rest two points.

12. As a final result report must contain diagram of vectors distribution (directions and magnitudes in three given points) on a desktop in the scale.

13. Conclude about the proper cause of difference of directions or magnitudes of these vectors in various points.

7. Test questions

1. What is magnetic field induction?

2. What is magnetic field intensity?

3. What are the magnetic field lines?

4. Draw field lines for a circular current. How to determine direction of intensity vector in the center of a circular current?

5. Write the formula for calculation of intensity in the center and on the axis of circular current.

6. What are the main features of magnetic field lines with respect to electrostatic field lines?

7. What is superposition principle? How the resultant magnetic intensity can be determined if the elementary intensities of each of elements of current are given.

8. How to determine the direction and magnitude of horizontal component of Earth’s magnetic field intensity by tangent-compass? Draw a scheme. Derive a calculation formula.

8. Content of the report

Homework to laboratory work № 3-1

(Answers on test questions from p.50)

…

Laboratory work № 3-1 implementation protocol

1) Тopic: STUDYING OF A MAGNETIC FIELD

VIA THE TANGENT-COMPASS

2) Goal:

1 Study of method of a vector diagrams for representation of force fields.

2 Finding the horizontal component of a magnetic field intensity vector in the laboratory via tangent-compass.

3) Scheme of laboratory research facility:

4) Table of measuring instruments:

№	Name	Type	Serial number	Grid limit	Grid unit	Accuracy class (absolute error)
1	Miliampermeter
	Four-decade resistors box R3
2	Tangent-compass			360o	5 o	5 o
3	Ruler

5) Equations for calculations:

Horizontal component of Earth’s magnetic field

,

where I – a current through the coil of tangent-compass; N – number of winds of a coil; D – diameter of a coil;  – angle of deviation of a needle when the current turn on from its zero-current position.

6) Table of measurements

N = 100; D = … mm.

№	,o	I, mA	, o	Hh, A / m
1.
2.
3.

7) Final results as a diagram:

8) Conclusions:

10) Data: “___” _____20___. Work done by: ______ Work checked by:

(Surname, readable)

LABORATORY WORK №3-4

1. Topic: STUDYING MAGNETIC FIELD IN FERROMAGNETS

2. Goal of the work:

2.1. Study magnetic field induction dependence in ferromagnets on magnetic field intensity magnitude.

2.2. Study magnetic permeability dependence in ferromagnets on magnetic field intensity magnitude.

3. Main concepts

3.1. Difference between the magnetic intensity and magnetic induction

The magnetic field is being characterized by two main quantities: vector of magnetic induction and vector of magnetic intensity.

Magnetic induction B is a force characteristic of magnetic field, because its magnitude is equal to the force which acts on unit element of current oriented perpendicularly to the vector of magnetic induction (85). Both magnetic induction and magnetic force are being determined by macro-currents in wires and by atomic micro-currents of medium, therefore both depend on magnetic permeability of medium .

Magnetic intensity H is additional quantity which characterize only external magnetic field of macro-currents in wires and is independent from medium in which magnetic field occurs (88). For example in center of circular current (91) we obtain:

=> and [H]=. (96)

Absolute value of magnetic intensity in center of circular current of unit diameter is equal to simply value of current. From (96) we can see, that the SI unit for magnetic intensity is ampere per meter (A/ m).

Magnetic induction in center of circular current:

. (97)

And, if circular current coats the iron core (3000), then in center of core the magnetic induction approximately 3000 times greater, than in air.

Permeability of medium  is a ratio between the magnetic force in medium and magnetic forcr in vacuum:

; []=1, (98)

it shows in how many times the magnetic induction in given medium is more, htan in vacuum. Permeability of medium is a dimensionless quantity.