List of Physics Laboratory Apparatus and Their Uses

Protractor

In physics and mathematics, a protractor is an instrument used to measure angles. It’s a D-shaped device with 18 divisions carved on it, each 10 degrees apart. It is used to measure angles in physics labs for a variety of purposes. In optics, for example, a protractor is used to determine the angle of incidence, refraction, or reflection of a light beam.

Stopwatch

A laboratory stopwatch is used to measure the time intervals or the time taken by an object for its displacement. It is used to measure the amount of time that elapses between its activation and deactivation.

Spring Balance

Spring balance is a device which consists of a hook attached to one end of the spring and is used for measuring the weights of various objects. The mass is hung on the hook and it moves downwards due to the gravitational force exerted by the object, which in turn pulls the spring downwards giving us the accurate mass of the object with the help of scales present on the spring balance.

Spherometer

A spherometer is a device which is used to measure the precise radius of the curvature of either a sphere or a curved surface, for example, the radius of curvature of lenses and spherical mirrors can also be measured using spherometers.

Triple beam balance

Triple beam balance is an apparatus used in laboratories to measure the mass of various objects. It consists of three beams, out of which one beam measures from 0 – 10 grams in 0.1 g increments, another beam measures from 0 – 100 grams in 10 g increments, and the third beam measures from 0 -600 grams in 100 g increments.

Speedometer

Speedometers are used to measure the instantaneous speed of an object. They are used in automobile industries for measuring the speed of the vehicle.

Sextant

A sextant is an instrument that is used to determine the altitude of far objects by measuring the angular difference between two lines of sight. Originally designed for navigation purposes, it has an arc of 60 degrees (one-sixth of a circle) and hence the name sextant; however, modern sextants have various angles. The sextant is composed of two mirrors, the horizon glass in which only the lower half is silvered, and the index mirror that can be rotated about an axis perpendicular to the plane of the instrument. An arm attached to the index mirror sweeps around the calibrated arc, on which the angles are engraved. The instrument’s horizon glass is aimed at the bottom reference point or horizon, and the arm is rotated until the reflection of the top reference point, whose altitude is to be calculated, on the index glass aligns with the horizontal line of sight (the horizon). After careful adjustment, the angular difference can be noted down and distance can be calculated with the help of trigonometry.

2. Optical equipment

Lenses

Lenses are defined as optical devices which focus or disperse light beams through the refraction of light. Lenses are transparent and usually circular in shape having two polished surfaces, either or both of which are curved and may be either convex (bulging/diverging) or concave (depressed/converging). They are used in laboratories for understanding the concepts of the refraction of light.

Concave

A concave lens is a lens that diverges the beam of light which has been passed through it. It is characterized by inside curved lenses either on both or one side of the lens. The images formed from concave lenses are sharp, upright, diminished, and virtual. Concave lenses are also used in binoculars, telescopes, cameras, flashlights, and eyeglasses, and in treating several eye disorders like short-sightedness or myopia. These types of lenses are used in physics laboratories to learn the concepts of the refraction of light.

Convex

Convex lenses are the type of lenses that converges the ray of light to form sharp images of the object. Convex lenses are thicker at the center and thin at the edges. When parallel rays of light pass through such lenses, the rays converge and meet at a common point behind them This point is known as a focal point. Convex lenses can produce both real and virtual images. Convex lenses are used in microscopes, magnifying glasses, camera lenses, and to correct hypermetropia (an eye disorder).

 

Prism

A prism is a triangular, 3-dimensional piece of glass or transparent material which is used in a physics laboratory for analyzing and studying the concepts of refraction. When a white ray of light is passed through a prism it refracts and splits into its spectrum of colors (violet, indigo, blue, green, yellow, orange, and red). This splitting of light into its spectrum colors is called as dispersion of light. Prisms are used in certain spectroscopes, and they can also be useful in binoculars as they can reverse the direction of light by internal reflection.

Mirror

Mirrors play a vital role in understanding the concepts of reflection of light and are therefore widely used in physics laboratories. Mirrors can be flat or spherical. The mirrors which we use on a daily basis in our houses are an example of flat mirrors, while spherical mirrors are of two types concave and convex. To understand the concepts of spherical mirrors a large shining spoon is the best example. One surface of such spoons is convex and the other side is a concave mirror.

Flat mirror

Flat mirrors (plane mirrors) are flat, smooth, and reflective surfaces. They are the only type of mirrors which produces an image that is virtual, upright, laterally inverted, and of the same size as the object, irrespective of the shape, size, and distance of an object from the mirror. Flat mirrors are the most common types of mirrors we use on a daily basis.

Concave mirror

Concave mirrors are converging surfaces that are used widely in automobiles and motor vehicles headlights, torchlights, head mirrors, solar furnaces, microscopes, telescopes, railway engines, etc. as reflectors. They are bent inwards which helps the mirror to converge the incident light. The parallel rays of light fall on the mirror and they converge at a point called the focus point. The image formed by concave mirrors can be both real as well as virtual depending on the positioning of the object as shown below.

Convex mirror

Convex mirrors always form virtual, erect, and diminished images, irrespective of the position of the object. Convex mirrors have a wide range of applications which includes a rear-view mirror in automobiles, sunglasses, street-light reflectors, magnifying glasses, microscopes, stores, hospitals, etc.

Optical Bench

An optical bench is a long horizontal bench consisting of two iron support bars, which is used to perform fundamental experiments of optics such as image formation, reflection, refraction, and more. Several objects such as lenses, image pins, object pins, mirrors, etc., can be mounted on the two bars with the help of the clamps. The clamps have a mark engraved on them which should be aligned with one of the rods that contain the scale markings. Also, there are leveling screws present on the four legs of the optical bench, which can be used to level the bench on an uneven surface. Optical benches are used for the precise positioning of light sources, screens, and optical instruments.

Glass slab

A glass slab is a cuboidal-shaped, 3-dimensional material made of glass and is widely used in physics for pin method experiments and understanding refraction phenomena. It is also used for providing refractive law and measuring refractive index.

3. Electrical equipment

Rheostats

A rheostat is a variable resistor which is used to control the current by varying the resistance. It works on the basic principle of Ohm’s law, which states that the resistance and current are inversely proportional to each other. Rheostats are used widely to adjust generator characteristics, dim lights, and start or control the speed of motors.

Multimeter

A multimeter is a device that combines several measurement functions in one unit and can be used to check the conductors, the continuity of the circuit, measuring the voltage in the socket or the battery level of the car. A normal multimeter may possess the abilities to measure voltage, current, and resistance.

Voltmeter

A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit. An analog voltmeter moves a pointer across a scale in proportion to the circuit’s voltage; a digital voltmeter provides a numerical display. Any measurement that can be converted to voltage can be displayed on a meter that is properly calibrated; such measurements include pressure, temperature, and flow.

Ammeter

An Ammeter is a measuring instrument used to find the strength of the current flowing around an electrical circuit when connected in series with the part of the circuit being measured. To measure a device’s current, it must be connected in series to that device. This is necessary because objects in a series experience the same current. They must not be connected to a voltage source, ammeters are designed to work under a minimal burden, (which refers to the voltage drop across the ammeter, typically a small fraction of a volt).

Decade Box

A decade box is a piece of instrumentation that can be used to replace the interchanging of distinct values of certain passive components with a single variable output during the prototyping of electrical circuits. Strings of varying lengths Resistance, capacitance, and inductance are all measured in decade boxes, and their values can be changed incrementally by turning a knob or switching contacts along with a series of the equivalent components. The interface of these devices is usually dials or variable tape counters, and they are operated in-circuit without the necessity of an external power supply.

Galvanometer

Analog meters have needles that swivel to point at numbers on a scale, as opposed to digital meters, which have numerical readouts. The heart of most analog meters is a device called a galvanometer, denoted by G. Current flow through a galvanometer, I_G, produces a proportional movement, or deflection, of the needle. The two crucial characteristics of any galvanometer are its resistance and its current sensitivity. Current sensitivity is the current that gives a full-scale deflection of the galvanometer’s needle, in other words, the maximum current that the instrument can measure. For example, a galvanometer with a current sensitivity of 50 μA has a maximum deflection of its needle when 50 μA flows through it, is at the scale’s halfway point when 25 μA flows through it, and so on. If such a galvanometer has a 25-Ω resistance, then a voltage of only V = IR = (50 μA)(25 Ω) = 1.25 mV produces a full-scale reading. By connecting resistors to this galvanometer in different ways, you can use it as either a voltmeter or ammeter to measure a broad range of voltages or currents.

Ballistic Galvanometer

The ballistic galvanometer is a type of galvanometer that is used to estimate the amount of charge flowing through it. The ballistic galvanometer operates on a fairly simple concept. It is determined by the coil’s deflection, which is proportional to the charge that travels through it. Regardless of current, the galvanometer measures the majority of the charge that goes through it. The ballistic galvanometer is made out of a copper wire coil wound on the galvanometer’s non-conducting frame. The coil is suspended between the north and south poles of a magnet by phosphorous bronze. The iron core is placed within the coil to increase the magnetic flux. The spring is connected to the lower half of the coil. This spring is responsible for recovering the coil’s torque. When a charge flows through a galvanometer, the coil begins to move and the galvanometer receives an impulse. The coil’s impulse is proportional to the charges that travel through it. The galvanometer’s real reading is obtained by utilizing a coil with a high moment of inertia. The term “moment of inertia” refers to the body’s resistance to angular movement. The oscillations of a coil with a high moment of inertia are considerable. As a result, a precise reading is acquired.

A Wein’s bridge, also known as Wein’s Robinson frequency bridge, is an AC circuit for determining the value of an unknown frequency. The bridge measures the frequencies from 100Hz to 100kHz. The accuracy of the bridges lies between 0.1 to 0.5 percent. The bridge is used for various other applications like capacitance measurement, the harmonic distortion analyzer, and the HF frequency oscillator. The bridge consists of four resistors and two capacitors. The Wien Bridge oscillator is a two-stage RC coupled amplifier circuit that has good stability at its resonant frequency, low distortion, and is very easy to tune making it a popular circuit as an audio frequency oscillator but the phase shift of the output signal is considerably different from the previous phase shift RC Oscillator. The Wien Bridge Oscillator uses a feedback circuit consisting of a series RC circuit connected with a parallel RC of the same component values producing a phase delay or phase advance circuit depending upon the frequency.

Anderson Bridge

AC bridges are often used to measure the value of the unknown impedance (self/mutual inductance of inductors or capacitance of capacitors accurately). A large number of AC bridges are available and Anderson’s Bridge is an AC bridge used to measure the self-inductance of the coil. It is a modification of Wheatstone’s Bridge. It enables us to measure the inductance of a coil using capacitors and resistors and does not require repeated balancing of the bridge. The bridge is balanced by a steady current by replacing the headphone H by moving the coil galvanometer and A.C source by a battery. This is done by adjusting the variable resistance, r. After a steady balance has been obtained, inductive balance is obtained by using the A.C. source and headphones. Sometimes it may be impossible to obtain the balance by varying r and S. Then the formula for L with a value of RQ which satisfies the formula for S may require a negative value of r. If the product  CRC is greater than L, then variable resistance r will be a negative quantity. It will, therefore, not be possible to obtain a balance point under such conditions. Hence it is desirable to know the value of L approximately so that CRQ is less than L. A balance is then obtained with a positive value of r.  The value of P and R should then be adjusted so that r is a positive quantity and a balance can be obtained by varying the value of r.

Maxwell Bridge

Maxwell’s bridge is also known as Maxwell’s Wein bridge or modified form of Wheatstone bridge or Maxwell’s inductance capacitance bridge, consists of four arms used to measure unknown inductances in terms of calibrated capacitances and resistances. It can be used to measure unknown inductance values and compares them with the standard value. It works on the principle of comparison of known and unknown inductance values. It uses the null deflection method to calculate inductance with a parallel calibrated resistor and capacitor. Maxwell’s bridge circuit is said to be in resonance if the positive phase angle of an inductive impedance is compensated with the negative phase angle of the capacitive impedance (connected in the opposite arm). Hence there will be no current flowing through the circuit and no potential across the null detector.

Battery eliminator

A battery eliminator is a device that converts high-voltage alternating current into low-voltage direct current. It is an alternative to ordinary batteries as a power source for devices like radio receivers AM/ FM, tape recorders, calculators, and other low-power operated equipment.

Daniell cell

Daniell cell is an electrochemical cell and is one of the best examples of the galvanic cell which converts chemical energy into electrical energy. Numerous chemical reactions are carried out by Daniell cells to produce electricity.  Its prominent use is to generate or store electricity. It consists of two different electrodes Zn and Cu are placed in their own ion solution ZnSO_{4}  and CuSO_{4} respectively. Daniell cells are used in battery development and electrical telegraphy.

Meter bridge

A meter bridge works on the basic principle of a balanced Wheatstone bridge, therefore it is also known as a Wheatstone meter bridge. It is used to calculate the unknown resistance of a  conductor with high precision and contains a wire of length 1 meter. The formula for calculating the unknown resistance is ρ=Lπr2X.

Leclanché cell

A leclanche cell is a primary cell which consists of a glass vessel containing ammonium chloride which acts as an electrolyte. It contains a zinc rod (negative electrode) and a porous pot in which a carbon rod is placed which is packed around a mixture of powdered carbon and magnesium dioxide. It is used in telegraphy, electric bell, and signaling work; and for work where intermittent and the low current was needed.

Ohm’s law apparatus

Ohm’s law states that resistance and current are inversely proportional to each other, and this can be stated by Ohm’s formula V=IR. 

where,

R= resistance

V =  voltage

I =  current

Ohm’s law apparatus is used in laboratories to demonstrate the interdependence of current, voltage, and resistance.

Bread Board

A breadboard is a rectangular plastic board with small holes to insert electronic components and an interconnected grid that connects the components accordingly. It is used to create temporary circuits for testing or experimenting with new ideas. Because no soldering is required, changing connections and replacing components is simple. The parts are not ruined and can be reused. Almost every new idea in electronics begins on the breadboard as a test circuit.

Thyratron Valve

A thyratron valve is a gas-filled relay made up of a thermionic valve, typically a triode. A discharge begins when a positive pulse is applied to a properly biassed thyratron, and it continues until the anode voltage is lowered. The silicon-controlled rectifier, a solid-state equivalent, has now taken its place.

4. Semiconductor Devices

Thyristor

In the same way that a thyratron valve controls the anode-cathode current, a thyristor is a signal applied to a third electrode (the gate) that controls the anode-cathode current in a silicon-controlled rectifier. It normally comprises a four-layer chip with three p-n junctions.

 

Diode

A diode is a semiconductor that functions as a current one-way switch. It permits current to flow freely in one direction while restricting current flow in the other. Because they convert alternating current (ac) to pulsing direct current, diodes are also known as rectifiers (dc). The types, voltages, and current capacities of diodes are all rated. The anode (positive lead) and cathode (negative lead) of a diode define its polarity (negative lead). When a positive voltage is given to the anode, most diodes enable the current to flow.

Photodiode

The photodiode is a type of light sensor that turns light energy into electricity (voltage or current). A photodiode is a PN junction semi-conducting device. There is an inherent layer between the p (positive) and n (negative) layers. To generate electric current, a photodiode accepts light energy as an input. The photodetector, Photo Sensor, or Light Detector are all terms for the same thing. The p – side of the photodiode is connected to the negative terminal of the battery (or the power supply) and the n – side to the positive terminal of the battery. Silicon, germanium, indium gallium arsenide phosphide, and indium gallium are all common photodiode materials.

Zener Diode

A Zener Diode is a type of semiconductor device that consists of a p-n junction diode with high doping concentrations on either side of the junction. It often acts as a voltage regulator and serves to safeguard the circuit from damage. The Zener diode, unlike a conventional diode, allows current to flow in both directions, giving it two operational modes: forward-biased and reverse-biased. When a Zener diode is reverse-biased, no current can flow until the circuit reaches a certain voltage called the Zener breakdown voltage. A Zener diode with a breakdown value of 5V, for example, will not allow the current to flow in the reverse direction until the source voltage is greater than 5V. This property allows us to set a reference voltage regulator in a circuit, which will bypass the extra voltage during the upsurge.

Light Emitting Diode (LED)

In the domain of electronics, light-emitting diodes, or LEDs, are a variety of tasks on a variety of devices. They generate numbers on digital clocks, relay data from remote controllers, illuminate watches, and notify you when your appliances are turned on. When they’re all put together, they may make graphics on a big screen or light up a traffic signal. LEDs are just little light bulbs that can be easily integrated into an electrical circuit. They don’t have filaments that burn out, they require less electricity, and they don’t become as hot as incandescent bulbs.

Triode

A triode is a three-electrode semiconductor device. After passing through the negatively biassed control grid, electrons created by the heated cathode flow to the anode. The anode current fluctuates dramatically when small voltage changes are overlaid on the grid bias. As a result, the triode was the first electrical device that could amplify signals. Except when high power (radio-frequency transmitters producing more than 1kW in power) is necessary, it has been replaced by the transistor.

Transistor

A transistor is a semiconductor device that can conduct as well as insulate electrical current or voltage. A transistor is a switch and an amplifier in one. A transistor, in simple terms, is a small device that is used to control or regulate the flow of electronic impulses. Transistors are one of the most important components in most modern electrical gadgets. The transistor, invented in 1947 by three American scientists John Bardeen, Walter Brattain, and William Shockley, is regarded as one of the most important inventions in science history.

Capacitor

A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors can be thin films of metal, aluminum foil, or disks, etc. The ‘nonconducting’ dielectric acts to increase the capacitor’s charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.

Resistor

Resistors are special components that are created for the sole purpose of providing a precise amount of resistance for use in a circuit. They’re usually made of metal wire or carbon, and they’re designed to keep a constant resistance value across a wide range of environmental circumstances. The resistor’s ability to reduce the current is called resistance and is measured in units of ohms (symbol: Ω). If we make an analogy to water flow through pipes, the resistor is a thin pipe that reduces the water Unlike lamps, they do not create light but they do produce heat when electric power is expended in a functioning circuit. Typically, however, the goal of a resistor is to supply a specific amount of electrical resistance rather than to produce usable heat.

5. Gravity-related apparatus

Pendulum

A pendulum is a rigid body that swings around a fixed point. An ideal simple pendulum consists of a bob of small mass attached at the end of a string or massless wire that oscillates back and forth through a small angle about the point of suspension. This device follows a simple harmonic motion and has a time period of 2π√{\frac{l}{g}}, where l is the length of the string and g is the acceleration due to gravity. A compound pendulum, on the other hand, is a rigid body that swings about a point within it, e.g., a point at the center of the string. Although the compound pendulum also follows a simple harmonic motion, its time period is given by T =  2π√{\frac{l({h}^{2}+{k}^{2})}{hgl}}, where k is the radius of gyration about an axis through the center of mass and h is the distance from the pivot to the center of the mass. Historically, pendulums were used to determine the acceleration due to gravity at the different geological positions; however, in a physics lab, they are used to demonstrate the proof of Newton’s first law of motion or timekeeping. A particular case of compound pendulum, known as a bar pendulum, is used to determine the acceleration due to gravity, the radius of gyration, and the moment of inertia of the bar about an axis through the center of gravity.

Kater’s Pendulum

Kater’s pendulum is a complex pendulum designed by Henry Kater, a British physicist, to measure the acceleration of free fall. The apparatus consists of two adjustable knife edges and three weights on a metal bar, with two weights affixed towards the ends along with the knife edges, and one adjustable weight affixed at the center of gravity of the pendulum. The bar is pivoted from each knife edge in turn, and the position of the weight at the center is adjusted such that the pendulum’s period is the same on both pivots. The time period is then determined using the simple pendulum formula, which allows g to be calculated.

Parallelogram apparatus

Gravesand’s apparatus consists of a board (26″ x 20″ x 0.5″), 2 pulleys on clamps, iron nickel-plated hangers, and 12 slotted weights which weigh 50g each. This apparatus is widely used in physics to study the parallelogram law of forces.  In this apparatus, two pulleys are fitted at the same level, and three sets of slotted weights are hung to these pulleys to determine and verify the parallelogram law of vectors. This apparatus states that at equilibrium, the vector sum of forces experienced by the two slotted weights at the adjacent is equal to the force experienced by the mass in the middle.

6. Waves and sound related

Tuning fork

A tuning fork is a U-shaped bar of elastic metal that consists of two-pronged forks. The U-shaped arm is called a prong, whereas the handle is termed as the stem. A tuning fork is an acoustic resonator that produces a pure and fixed tone. It is usually made up of steel or aluminum provided with a steel handle. It is traditionally used to tune musical instruments. Tuning forks also has medical uses, for example, doctors sometimes use tuning forks to determine weather the bone is fractured or not.

Vibration generator

A vibration generator contains a resonator that is used to amplify the vibration source and a transducer device that transfers vibrations into electrical energy.  These generators have a wide range of applications in Chemicals, fertilizers, Petrochemicals, Plastic, Mining, Food Processing, and Packaging industries.

 

Sonometer

A sonometer is an instrument consisting essentially of a hollow-sounding box with two bridges attached to its top. Originally called the monochord, the sonometer was once widely used as a tuning tool but is now exclusively employed in physics laboratories to find the unknown frequency of a tuning fork and verify the laws of lengths, masses, and tension. The string fixed to the one end of the box is stretched between the two bridges, such that the free end can run over a pulley and support a measured load. When the string is plucked, the frequency of the note can be matched with that of the tuning fork. It can be used to verify that the frequency (f) of the stretched string is given by

f={\frac{1}{2l}}{√\frac{T}{m}}

Where l is the length of the string, m is the mass per unit length, and T is the tension.

Resonance apparatus

A resonance apparatus is used to identify the resonance positions in air columns which makes it feasible to calculate the speed of sound using water level and tuning fork frequency.

 

7. Heat and thermodynamics

Copper calorimeter

Copper is a good conductor of heat and is therefore the most suited element for making calorimeters. It readily reaches the equilibrium temperature by absorbing heat as it has a low specific heat capacity. This apparatus is used for measuring the heat of chemical reactions, physical changes, and heat capacity.

Steam boiler

A steam boiler is a closed vessel used to heat water or other liquids. It is made up of copper and the steam generated may be used for numerous purposes including water heating, central heating, boiler-based power generation, cooking, and sanitation. One of the major applications of steam boilers includes HVAC systems.

Thermometer

The thermometer is a device that contains mercury and is used to check the temperatures of materials other than the human body temperature. It enhances precision in applications, such as experiment monitoring, instrument calibration, materials testing, and maintaining a sterile work environment.

Thermal Conductivity Detector (TCD)

A thermal conductivity detector, as the name suggests, is mainly used to measure the thermal conductivity of carrier gas/analyte mixture leaving the GC column. It can be used for both organic and inorganic compounds. TCD is most commonly used in gas chromatography technique to detect various inorganic gases (argon, nitrogen, hydrogen, carbon dioxide) and small hydrocarbon molecules.

Density ball

It is used in laboratories to explain the effect of temperature on the density of the liquid. When this ball is placed on a room-temperature water surface it floats because the density of the ball is lighter than that of water, but when this water is heated the ball sinks. This happens due to the alleviating/decreasing density of the ball.

Lee’s Apparatus

The thermal conductivity of a poorly conducting medium, such as glass, wood, or polymer, is measured using Lee’s Disc method. Although it was first described around the year 1898 by English scientist Lee, there is little knowledge regarding the method’s origins. This is a steady-state method that was one of the first methods used to evaluate thermal conductivity that yielded reliable results. The experimental setup must attain equilibrium before any computations can be performed using steady-state methods. Transient approaches do not require equilibrium before computations because they are based on temperature versus time curves plotted during the heating process.

8. Magnetic equipment

Compass

A compass is a magnetic device that is mainly used for navigation purposes. It consists of a magnetized needle which is used to ascertain a direction. A compass helps to determine the direction on the Earth’s surface with the help of a magnetic needle which aligns itself with the earth’s magnetic field. It has a wide range of applications and is used in aircraft, ships, land vehicles, and by surveyors.

Bar magnets

Bar magnets are found in physics laboratories for understanding the concepts of magnets. A bar magnet consists of a north pole and a south pole. When two bar magnets are placed together then like poles repel each other and unlike poles attract each other.

Iron fillings

Iron fillings are powder-like small pieces of ferromagnetic/iron particles that play a vital role in various magnetic experiments. They are used in schools to test their reaction to magnets. A magnetic field induces each particle of the iron fillings to act as a tiny bar magnet, and each particle has its own north and south pole. The north poles and south poles of these tiny magnets attach and form chains of fillings parallel to the magnetic field.