NCERT MCQ Solutions for Class 8 Science Curiosity Chapter 4 Electricity: Magnetic and Heating Effects

When an electric current flows through a conductor like a wire, it produces a magnetic field around it. This phenomenon is called the magnetic effect of electric current. This invisible region can be detected by the deflection of a magnetic compass placed nearby.

When electric current flows through a nichrome wire, it offers resistance, which converts electrical energy into heat energy. This causes the wire to become warm. This is known as the heating effect of electric current and is observed using safe teacher-supervised experiments. 

A current-carrying coil behaves like a magnet and is called an electromagnet. Its describes how paper clips cling to the coil when current flows and fall off when it is disconnected, proving that electricity can create magnetism through the formation of temporary magnets.

The strength of an electromagnet can be increased by increasing the number of turns in the wire coil or increasing the electric current. More turns mean more magnetic field lines, leading to stronger magnetic attraction as shown in the compass deflection experiment.

Most practical electromagnets have an iron core because it enhances the magnetic field produced by the coil. The presence of an iron core increases the strength of the magnetic effect and helps the coil lift heavier objects like iron paper clips.

Appliances like electric irons and stoves work using the heating effect of electric current. When current flows through a heating element, such as a nichrome wire, it generates heat. This heat is used for purposes like ironing clothes or cooking food.

The compass needle deflects when placed near a wire through which current flows, indicating the presence of a magnetic field. This magnetic field affects the needle since it is a tiny magnet, thus proving the magnetic effect of electric current.

The magnetic field is the area around a magnet or a current-carrying wire where its magnetic influence can be detected. Using the deflection of a compass needle, which indicates the presence and direction of the magnetic field.

Nichrome is preferred in electric heating devices because it has higher resistance and generates more heat for a given current. Classroom experiments where nichrome wire gets warmer than copper wire when the same current flows through them.

The amount of heat produced depends on the material, length, thickness of the wire, and duration of current flow. The colour of the wire is not mentioned as a relevant factor in determining how much heat is generated by the electric current.

An electric cell as a device that produces electric current using chemical reactions. Examples include dry cells and voltaic cells.
These cells have electrodes and electrolytes that interact chemically to create a flow of electricity through a closed circuit.

A Voltaic cell, also called a Galvanic cell, uses two different metal electrodes dipped in an electrolyte.
This setup creates electricity through chemical reactions. The historical discovery and explains its construction using examples like copper and iron plates in salt solutions.

Alessandro Volta with inventing the first battery. He demonstrated that electricity could be produced using two different metals and an electrolyte.
His invention, called the Voltaic cell, marked the beginning of modern electrical energy storage and production.

Unlike voltaic cells with liquid electrolytes, dry cells use a thick moist paste. This makes them leak-proof and portable. Dry cells consist of a zinc container, carbon rod and paste-like electrolyte, making them suitable for use in torches and remote controls.

In the structure of a dry cell explained in the chapter, the zinc container serves as the negative terminal. The positive terminal is the carbon rod in the centre. The chemical reactions between these terminals and the electrolyte produce the electric current.

The carbon rod placed at the center of the dry cell is the positive terminal. It collects electrons from the electrolyte and passes them to the external circuit. This setup enables current to flow from the positive to the negative terminal.

Connecting a wire directly across the terminals of a cell causes a short circuit. This can lead to overheating, rapid depletion of the cell or even damage.
It bypasses the electrical device and allows uncontrolled current flow.

An electromagnet is a temporary magnet created when electric current flows through a coil of wire, usually wrapped around an iron core. It is demonstrates that such magnets lose their magnetism once the current is stopped and regain it when current flows again.

Dry cells produce direct current, meaning current flows in only one direction. This steady flow is suitable for powering devices like torches and radios. Alternating current (AC), which changes direction, is not produced by dry cells.

When electric current flows through the filament in a bulb, it offers resistance and gets heated.
The heat causes the filament to glow and emit light. This example to explain the heating effect of electric current and its practical use.

The carbon rod is surrounded by a layer of manganese dioxide. This chemical acts as a depolarizer and helps maintain the chemical reaction by absorbing hydrogen gas that would otherwise interfere with current production.

The zinc container also serves as the negative terminal and holds the electrolyte. If damaged, the electrolyte paste can leak out, damaging the device.
The zinc gradually corrodes during cell use, which limits the dry cell’s life.

Dry cells are compact, sealed and use a moist paste instead of liquid, making them safer and easier to use in portable devices.
The bulkier, leak-prone voltaic cells, showing the advantages of dry cells in everyday appliances.

The heat generated in a wire depends on the current and the resistance. Using higher resistance material like nichrome or increasing the current passing through the wire will increase the amount of heat generated, demonstrating the heating effect of electric current.

Electric current is measured in amperes (A). It quantifies the flow of electric charge through a conductor. Other units like volts (V) measure potential difference and ohms (Ω) measure resistance. Ampere is the correct unit for current flow.

Hans Christian Oersted with discovering the magnetic effect of electric current. He observed that a magnetic compass needle deflected when placed near a current-carrying wire, proving the link between electricity and magnetism for the first time in 1820.

Iron is used as the core material in electromagnets because it enhances magnetic field strength.
An iron nail wrapped with wire becomes a stronger magnet when current passes through it compared to using no core or non-magnetic materials.

The electric bell is a practical application of electromagnets. The electromagnet attracts a metal strip when current flows, which strikes the bell and breaks the circuit, creating a repeated ringing effect through continuous magnetic pull and release.

Resistance in a wire opposes the flow of electric current. This opposition causes some electrical energy to convert into heat energy. This principle through examples like heating elements in electric irons or heaters made of high-resistance materials like nichrome.

A circuit is complete when it forms a closed loop, allowing electric current to flow from the source to the device and back.
Examples like bulb connections and dry cell arrangements that must be closed for proper functioning.