Effects of Electric Current - Class 7 Notes & Olympiad Questions

Effects of Electric Current

a) Electric current is the flow of electric charges, usually in the form of electrons, through a conductor like a wire.
b) These charges can do different things when they flow through the wire. Some of these effects are lighting effect, heating effect, chemical effect and magnetic effect.
c) These effects show us how electric current can do different things and have a big impact on our daily lives. Understanding them helps us appreciate the technology behind lights, heaters, and other electrical devices we use every day.

Lighting Effect

a) One of the most common and visible effects of electric current is the generation of light. When a high amount of electric current passes through certain materials, they emit light. This effect is used in various lighting devices, such as incandescent bulbs, fluorescent tubes, and LED lights.
b) In an incandescent bulb, an electric current flows through a thin filament made of tungsten. The filament becomes so hot that it glows and emits visible light. However, incandescent bulbs are not very energy-efficient and have largely been replaced by more efficient options.
c) LED (Light-Emitting Diode) lights are becoming increasingly popular due to their energy efficiency and long lifespan. LEDs work by passing an electric current through a semiconductor material. This causes the electrons to release energy in the form of photons, producing visible light. LEDs are used in various applications, including household lighting, displays, and automotive lighting.
d) Understanding the lighting effect of electric current helps us appreciate the technology behind different types of lighting and the importance of energy-efficient options for reducing electricity consumption and environmental impact.

Heating Effect

a) The heating effect of electric current is when electric charges flowing through a wire or a conductor produce heat.
b) When electric charges, which are tiny particles called electrons, move through a wire, they experience some resistance. This resistance is like a hurdle that the charges have to overcome as they move along the wire. While overcoming this hurdle, the charges collide with atoms or molecules in the wire, which causes them to transfer some of their energy.
c) This transfer of energy makes the atoms or molecules in the wire vibrate faster, and as a result, the wire starts to get hot. The more electric charges flow through the wire, and the higher the resistance, the hotter the wire gets.
d) This heating effect is essential in many everyday devices. For example, when you turn on an electric stove or use a toaster, electric current passes through a coil or an element inside them. The resistance in the coil or element causes the wire to heat up and transfer the heat to your food, toasting it or cooking it.
e) It's important to remember that the heating effect of electric current can be useful, but it can also be dangerous. That's why it's crucial to handle electrical devices carefully and follow safety precautions to avoid accidents.

Factors that Affect the Heat Produced in the Wire

a) The type of material the wire is made of: Different materials can affect how much heat is generated when electric charges flow through them. Some materials can handle more heat without getting too hot, while others might get hotter more quickly.

b) The length of the wire: The longer the wire, the more resistance it has, and the more heat is generated as electric charges pass through it. It's similar to how a longer path might slow you down when you're running. More heat is produced as the charges encounter more resistance along a longer wire.

c) The thickness of the wire: Thicker wires have less resistance compared to thinner wires. So, if the wire is thicker, it can allow more electric charges to flow through easily, resulting in less heat being generated. It's like how a wide road allows more cars to pass through quickly, causing less traffic and less heat.

The Electric Fuse and the Heating Effect of Current

An electric fuse is a safety device used to protect electrical circuits from too much current. It works by utilising the heating effect of current. They work based on the heating effect of current.

a) The fuse is made up of a thin wire or strip that is designed to melt or break when too much current passes through it.
b) When the current flowing through the fuse exceeds its rated capacity, the wire inside the fuse heats up due to the heating effect of the current.
c) As the wire gets hotter and hotter, it eventually melts or breaks, which opens the circuit and stops the flow of current.
d) By breaking the circuit, the fuse protects the electrical devices and wiring from damage caused by excessive current, and it also prevents potential hazards like fires.

So, the electric fuse uses the heating effect of current to keep electrical circuits safe by breaking the circuit when there's too much current flowing through it.

Chemical Effect

a) Electric current can cause chemical changes in certain substances. This is called the chemical effect of electric current or electrolysis.
b) Electrolysis is the process of using electric current to decompose a compound into its constituent elements or ions.
c) For example, when you pass an electric current through water, it splits into hydrogen and oxygen gases. This effect is used in various industrial processes, such as electroplating, where a layer of metal is deposited on an object.

Magnetic Effect

a) When electric current flows through a wire, something interesting happens. It creates a special force called a magnetic field around the wire. This is called the magnetic effect of electric current.
b) This discovery was made by a scientist named Hans Christian Oersted. He noticed that when an electric current flows through a wire, it can make a compass needle move. A compass needle usually points in a certain direction, but when it gets close to a wire with electric current, it changes its direction.
c) If we change the direction of the electric current in the wire, the compass needle will also change its direction.
d) However, when there is no electric current flowing through the wire, the compass needle doesn't show any movement. It only behaves like a magnet and affects the compass when there is an electric current flowing through the wire.
e) So, when electric current passes through a wire, it creates a magnetic field around it, and it can make a compass needle move. This magnetic effect is a fascinating way that electricity and magnetism are connected.

Application of Magnetic Effect of Electric Current

Electric Motors

a) Electric motors are everywhere around us! They use the magnetic effect of electric current to convert electrical energy into mechanical energy.
b) When electric current passes through a coil of wire placed in a magnetic field, it creates a force that causes the coil to spin.
c) This spinning motion is used to power various devices like fans, blenders, washing machines, and even electric cars.

Maglev Trains

a) Maglev (magnetic levitation) trains use the magnetic effect of electric current to achieve high speeds and a smooth, frictionless ride.
b) These trains are designed with powerful magnets both on the tracks and underneath the train.
c) By using the repulsion and attraction between the magnets, maglev trains can float just above the tracks, eliminating the need for wheels.

Electromagnets

a) An electromagnet is a type of magnet that harnesses the magnetic effect of electric current. It consists of a coil of insulated wire wound around a magnetic core, usually made of iron. When an electric current passes through the wire, it generates a magnetic field around the coil and induces magnetism in the core.
b) What sets electromagnets apart from permanent magnets is their temporary nature. The magnetism of an electromagnet is directly tied to the presence of electric current. Once the current is switched off, the magnetic properties of the electromagnet dissipate, and it reverts to a non-magnetic state.

c) The strength or magnetic field intensity of an electromagnet is influenced by two key factors:

1. The amount of electric current flowing through the wire: The greater the current, the stronger the magnetic field produced. This relationship follows a direct proportionality, meaning that increasing the current will result in a proportional increase in the magnetic field strength.
2. The number of turns of the wire in the coil: By increasing the number of turns in the coil, the magnetic field strength can be enhanced. This is because each turn contributes to the overall magnetic field generated, effectively amplifying the magnetism of the electromagnet.

These two factors, current flow, and coil turns, directly impact the effectiveness and power of the electromagnet, allowing for control over its magnetic properties.

d) Electromagnets are used in toys, cranes for lifting heavy objects, and electric bells for making sounds. They are also used by doctors in MRI machines to look inside our bodies and in electric motors for powering devices like fans and blenders.