Category Science

Inside many electric light bulbs is a wire called a filament, made of tungsten. When current is passed through the wire, it glows white hot, giving off light and some heat. As the oxygen has been removed from the bulb, combustion cannot take place, so the wire does not bum out immediately.

Electricity flows through a thin tungsten wire in the light bulb called the filament. The filament used in a bulb has a property called “resistance.” Resistance is the amount of friction that an object will put against electricity flowing through it. A filament has a lot of resistance to electricity. As a result of this resistance, the filament heat up and start glowing, converting electrical energy to light energy. This is because of the Joule-effect, which means that resistances heat up when an electrical current runs through them. This produces light and heat illuminating its surroundings.

The brightness of the filament can be varied by changing the amount of current flowing through it (the amperage), or the voltage between ends, as the amperage is related to the voltage by Ohm’s law. Also, as the filament ages, its brightness will diminish somewhat and its light will get redder and redder. Eventually, all filaments will slowly vaporize and fail due to the high temperature caused by the electricity flowing through it.

By design, a light bulb has no oxygen in it. The manufacturer fills it with an inert gas like argon or nitrogen. However, this does not prevent atoms from popping off the surface of the filament due to the intense heat. This makes the filament thinner and thinner. Eventually, it becomes so thin that it breaks. For a short period of time, the two broken ends are very close to each other, and electricity can jump across in a bright blue spark. However, the two broken ends soon fall away from each other, breaking the spark, and the bulb will light no more.

Light bulbs themselves, if used properly, are not dangerous. Although their primary function is to produce light energy, as a side effect they also produce heat.

Light bulbs are sold according to the number of watts they use – the higher the number, the brighter the bulb is, and the more energy it uses. Despite getting hot, light bulbs don’t explode. However, the outer glass of a light bulb which has been on for some time is quite hot, and can cause minor burns, or the broken edges might cut the skin.

Fleming’s right-hand rule enables you to tell in which direction a current flow in a wire that is moved in a magnetic field. Hold your hand as shown and point your thumb, in the direction of motion and your first finger in the direction of the magnetic field. Your second finger will then point in the direction in which current flows in the wire.

Physicists use a hand mnemonic known as the right-hand rule to help remember the direction of magnetic forces. To form the mnemonic, first make an L-shape with the thumb and first two fingers of your right hand. Then, point your middle finger perpendicular to your thumb and index finger.

The right-hand rule is based on the underlying physics that relates magnetic fields and the forces that they exert on moving charges—it just represents an easy way for physicists to remember the directions that things are supposed to point. Occasionally a physicist will accidentally use their left hand, causing them to predict that the magnetic force will point in a direction opposite the true direction!

Moving charges

When charges are sitting still, they are unaffected by magnetic fields, but as soon as they start to move, the magnetic field pushes on them. But, the direction in which the field pushes on charges is not the same as the direction of the magnetic field lines.

We can remember this diagram using the right-hand rule. If you point your pointer finger in the direction the positive charge is moving, and then your middle finger in the direction of the magnetic field, your thumb points in the direction of the magnetic force pushing on the moving charge. When you’re dealing with negative charges—like moving electrons—the force points in the opposite direction as your thumb.

Fleming’s left-hand rule enables you to use your hand to work out the direction of motion of a current-carrying wire in a magnetic field. Hold your hand as in the picture, with the first finger pointing in the direction of the magnetic field and your second finger in the direction of the electric current. Your thumb will now point in the direction of motion of the wire.

Fleming’s left-hand rule for electric motors is one of a pair of visual mnemonics, the other being Fleming’s right-hand rule (for generators). They were originated by John Ambrose Fleming, in the late 19th century, as a simple way of working out the direction of motion in an electric motor, or the direction of electric current in an electric generator.

Whenever a current carrying conductor comes under a magnetic field, there will be force acting on the conductor. The direction of this force can be found using Fleming’s Left Hand Rule (also known as ‘Fleming’s left-hand rule for motors’).

Similarly if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor. The direction of this force can be found using Fleming’s Right Hand Rule.

In both Fleming’s left and right hand rules, there is a relation between the magnetic field, the current and force. This relation is directionally determined by Fleming’s Left Hand rule and Fleming’s Right Hand rule respectively.

These rules do not determine the magnitude but instead show the direction of any of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known. Fleming’s Left-Hand rule is mainly applicable to electric motors and Fleming’s Right-Hand rule is mainly applicable to electric generators.

An electric motor uses a current and a magnetic field to create motion. A specially shaped coil of wire, called an armature, is positioned between the poles of a permanent magnet. When an electric current is fed into the wire, the coil becomes a magnet too and forces of attraction and repulsion between it and the permanent magnet cause the armature to move around its axis. A device called a commentator then reverses the current, so that the armature’s magnetic poles are reversed and it turns through 180 degrees. If the current is continually reversed, the armature is always turning on its axis. It is this motion that can be used to drive a huge number of machines, such as washing machines, hairdryers and food processors.

An electric motor creates rotational, or circular, motion. The central part of the motor is a cylinder called the armature or rotor. The armature holds the rest of the components and is also the part of the motor that spins. Around the armature is the stator, which holds insulated coils of wire, usually copper. When a current is applied to the motor, the stator generates the magnetic field that drives the armature. Depending on the design of the motor, you might also find brushes, or fine metal fibers that keep current running to the opposite side of the motor as it spins.

The basic motor runs on DC, or direct current, but other motors can run on AC, or alternating current. Batteries produce direct current, while the outlets in your home supply alternating. In order for a motor to run on AC, it requires two winding magnets that don’t touch. They move the motor through a phenomenon known as induction. These induction motors are brushless, since they don’t require the physical contact that the brush provides. Some DC motors are also brushless and instead use a switch that changes the polarity of the magnetic field to keep the motor running. Universal motors are induction motors that can use either source of power.

Now that you have the basic parts and principles, you can play with the concept at home. Make a coil from lower gauge copper wire and poke each end through an aluminum can to suspend it. Place a small, strong magnet on either side of the suspended coil to create a magnetic field. If you attach a battery to both cans using alligator clips, your coil will become an electromagnet and the copper wire rotor you created should start to spin.