Magnets are commonly found in motors, dynamos, refrigerators, debit and credit cards, as well as electronic equipment such as electric guitar pickups, stereo speakers, and computer hard drives. Magnets can be permanent, naturally formed, or electromagnet. An electromagnet creates a magnetic field when an electric current passes through a coil of wire that wraps around an iron core. There are several factors that affect the strength of a magnetic field and various ways to determine the strength of the field, and both are discussed in this article.
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Method 1 of 3: Determining Factors Affecting Magnetic Field Strength
Step 1. Consider the characteristics of the magnet
The properties of magnets are described using the following characteristics:
- The strength of the coercive magnetic field, abbreviated as Hc. This symbol reflects the point of demagnetization (loss of magnetic field) by another magnetic field. The higher the number, the harder the magnet is to remove.
- Residual magnetic flux density, abbreviated as Br. This is the maximum magnetic flux a magnet is capable of producing.
- Corresponding to the magnetic flux density is the overall energy density, abbreviated as Bmax. The higher the number, the stronger the magnet.
- The residual magnetic flux density temperature coefficient, abbreviated as Tcoef Br and expressed as a percentage of degrees Celsius, explains how the magnetic flux decreases as the magnetic temperature increases. A Tcoef Br of 0.1 means that if the temperature of the magnet increases by 100 degrees Celsius, the magnetic flux decreases by 10 percent.
- The maximum operating temperature (abbreviated as Tmax) is the highest temperature a magnet can operate without losing its field strength. Once the temperature of the magnet drops below Tmax, the magnet recovers its full magnetic field strength. If heated beyond Tmax, the magnet will lose some of its field permanently once cooled to normal operating temperature. However, if heated to a Curie temperature (abbreviated as Tcurie) the magnet will lose its magnetic power.
Step 2. Identify the materials for making permanent magnets
Permanent magnets are usually made of one of the following materials:
- Neodymium iron boron. This material has a magnetic flux density (12,800 gauss), a coercive magnetic field strength (12,300 oersted), and an overall energy density (40). This material has the lowest maximum operating temperature of 150 degrees Celsius and 310 degrees Celsius respectively, and a temperature coefficient of -0.12.
- Samarium cobalt has the second highest coercive field strength, at 9,200 oersted, but a magnetic flux density of 10,500 gauss and an overall energy density of 26. Its maximum operating temperature is much higher than that of neodymium iron boron at 300 degrees Celsius due to its Curie temperature of 750 degrees Celsius. Its temperature coefficient is 0.04.
- Alnico is an aluminum-nickel-cobalt alloy. This material has a magnetic flux density close to that of neodymium iron boron (12,500 gauss), but a coercive magnetic field strength of 640 oersted and an overall energy density of only 5.5. This material has a higher maximum operating temperature than samarium cobalt, at 540 degrees Celsius., as well as a higher Curie temperature of 860 degrees Celsius, and a temperature coefficient of 0.02.
- Ceramic and ferrite magnets have much lower flux densities and overall energy densities than other materials, at 3,900 gauss and 3.5. However, their magnetic flux densities are better than alnico, which is 3,200 oersted. This material has the same maximum operating temperature as samarium cobalt, but a much lower Curie temperature of 460 degrees Celsius, and a temperature coefficient of -0. 2. Thus, magnets lose their magnetic field strength more quickly in hot temperatures than other materials.
Step 3. Count the number of turns in the coil of the electromagnet
The more turns per core length, the greater the strength of the magnetic field. Commercial electromagnets have an adjustable sized core of one of the magnetic materials described above and a large coil around it. However, a simple electromagnet can be made by winding a wire around a nail and attaching the ends to a 1.5-volt battery.
Step 4. Check the amount of current flowing through the electromagnetic coil
We recommend that you use a multimeter. The greater the current, the stronger the magnetic field produced.
Ampere per meter (A/m) is another unit used to measure the strength of a magnetic field. This unit indicates that if the current, the number of coils, or both are increased, the strength of the magnetic field also increases
Method 2 of 3: Testing the Magnetic Field Range with a Paperclip
Step 1. Make a holder for the bar magnet
You can make a simple magnetic holder using clothespins and a styrofoam cup. This method is most suitable for teaching magnetic fields to elementary school students.
- Glue one long end of a clothesline to the bottom of the cup.
- Overturn the cup with the clothesline tongs on it and place it on the table.
- Clamp the magnets to the clothesline tongs.
Step 2. Bend the paper clip into a hook
The easiest way to do this is to pull the outer edge of the paper clip. This hook will hang a lot of paper clips.
Step 3. Continue adding paper clips to measure the strength of the magnet
Attach a bent paper clip to one of the poles of the magnet. hook part should hang freely. Hang the paper clip on the hook. Continue until the weight of the paper clip drops the hook.
Step 4. Record the number of paper clips that caused the hook to fall off
When the hook falls under the weight it is carrying, note the number of paper clips hanging on the hook.
Step 5. Adhere the masking tape to the bar magnet
Attach 3 small strips of masking tape to the bar magnet and hang the hooks back.
Step 6. Add a paper clip on the hook until it falls off the magnet
Repeat the previous paperclip method from the initial paperclip hook, until it finally falls off the magnet.
Step 7. Write down how many clips it takes to drop the hook
Make sure you record the number of strips of masking tape and paper clips used.
Step 8. Repeat the previous step several times with more masking tape
Each time, record the number of paper clips needed to fall off the magnet. You should notice that each time the tape is added, less clip is needed to drop the hook.
Method 3 of 3: Testing a Magnetic Field with a Gaussmeter
Step 1. Calculate the base or initial voltage/voltage
You can use a gaussmeter, also known as a magnetometer or an electromagnetic field (EMF) detector, which is a portable device that measures the strength and direction of a magnetic field. These devices are usually easy to buy and use. The gaussmeter method is suitable for teaching magnetic fields to middle and high school students. Here's how to use it:
- Set the maximum voltage of 10 volts DC (direct current).
- Read the voltage display with the meter away from the magnet. This is the base or initial voltage, represented as V0.
Step 2. Touch the meter sensor to one of the magnetic poles
In some gaussmeters, this sensor, called a Hall sensor, is made to integrate an electrical circuit chip so that you can touch a magnetic bar to the sensor.
Step 3. Record the new voltage
The voltage represented by V1 will increase or decrease, depending on the magnetic bar that touches the Hall sensor. If the voltage rises, the sensor touches the south finder magnetic pole. If the voltage drops, it means that the sensor is touching the north finder magnetic pole.
Step 4. Find the difference between the initial and new voltages
If the sensor is calibrated in millivolts, divide by 1,000 to convert millivolts to volts.
Step 5. Divide the result by the sensor sensitivity value
For example, if the sensor has a sensitivity of 5 millivolts per gauss, divide by 10. The value obtained is the strength of the magnetic field in gauss.
Step 6. Repeat the magnetic field strength test at various distances
Place the sensors at various different distances from the magnetic poles and record the results.
