Electric Current and Its Effects – Class 7 Science (Notes & Questions)

Notes: Electric Current and Its Effects

What is electric current? — Electric current is the flow of electric charge (usually electrons) through a conductor. In everyday circuits we usually speak of current as the flow of positive charge in a particular direction (conventional current). The unit of electric current is the ampere (A).

Sources of Electric Current

The most common sources of electric current for small circuits are cells and batteries. A cell converts chemical energy into electrical energy. When cells are connected in series they form a battery which supplies current to a circuit. Common batteries used in classrooms are dry cells (AA, AAA) and lead-acid batteries for bigger applications.

Electric Circuit and Its Components

An electric circuit is a closed path through which current flows. Basic components you will meet:

  • Cell / Battery: Source of electrical energy.
  • Conductor (wire): Path for current to flow.
  • Switch: Opens or closes the circuit to control current.
  • Bulb or resistor: A device that uses electrical energy (light, heat).
  • Ammeter: Measures current; connected in series.
  • Voltmeter: Measures potential difference (voltage); connected in parallel.

Symbols and Circuit Diagrams

Circuit diagrams use standard symbols to represent cells, wires, bulbs, switches, and meters. Learning and drawing neat circuit diagrams helps you quickly understand how devices are connected (series or parallel).

Conductors and Insulators

Materials that allow current to flow easily are called conductors (e.g., copper, aluminium). Materials that do not allow current to flow are called insulators (e.g., rubber, plastic, glass). Conductors are used for wiring; insulators are used to cover wires and for safety.

Direction of Current

Two ways to describe direction: conventional current (from positive to negative terminal) and electron flow (actual electrons move from negative to positive). For school-level circuits we normally use conventional current direction.

Series and Parallel Connections

In a series circuit, devices are connected end-to-end so current is same through all parts but voltage is divided. In a parallel circuit, devices are connected across the same two points so each device gets full voltage and current divides. Series bulbs get dimmer as more are added; parallel bulbs retain brightness.

Measuring Current and Voltage

An ammeter measures current and must be connected in series. A voltmeter measures voltage and must be connected across the component (in parallel). Always use meters with correct range to prevent damage.

Effects of Electric Current

1. Heating Effect

When current passes through a conductor, it produces heat (Joule heating). This effect is used in electric heaters, toasters, fuses, and electric bulbs (in filament lamps). A fuse uses a thin wire that melts if too much current passes, protecting the circuit.

2. Magnetic Effect

Electric current produces a magnetic field around the conductor. A coil of wire carrying current acts like a magnet (an electromagnet) when connected to a battery. This magnetic effect is used in electric bells, loudspeakers, and motors.

3. Chemical Effect

Passing current through certain liquids (electrolytes) causes chemical changes — this is electrolysis. It is used in electroplating, refining metals, and some storage batteries.

4. Luminous Effect

Some conductors (filaments, neon tubes, LEDs) produce light when current flows. This luminous effect is used in lamps and indicators.

5. Physiological Effect

Electric current can be harmful if it passes through the human body. Even small currents can cause a shock; larger currents can be fatal. This is why safety and insulation are critical.

Electromagnets and Their Uses

An electromagnet is made by winding a wire coil around an iron core and passing current through the coil. The core becomes magnetized only when current flows. Electromagnets are widely used in cranes for lifting scrap metal, in electric bells, relays, and MRI machines.

Practical Applications of Effects

  • Heating: Electric iron, geyser, toaster.
  • Magnetic: Motors, cranes, electric bell.
  • Chemical: Electroplating, battery charging.
  • Luminous: Bulbs and LEDs for lighting.

Precautions and Safety

Never touch exposed wires. Use insulated tools. Keep electrical devices away from water. Always switch off and unplug appliances before repairing. Use earthing and fuses to prevent shocks and fire. Teach children safe distance rules around high-voltage lines and household sockets.

Quick exam tip: For diagrams, label the battery, switch, bulb, and ammeter clearly. In short answers, always mention the effect (heating/magnetic/chemical) and give one real-life example.

Questions & Answers

MCQs (Choose the correct option)

1. Which material is the best conductor of electricity?

A. Rubber   B. Copper   C. Glass   D. Wood

Ans: B. Copper

2. The device used to open or close an electric circuit is called:

A. Ammeter   B. Switch   C. Voltmeter   D. Resistor

Ans: B. Switch

3. In which connection do bulbs glow with full brightness when connected to the same battery?

A. Series   B. Parallel   C. Series-parallel mix   D. None

Ans: B. Parallel

4. Which effect of electric current is used in an electric bell?

A. Heating   B. Magnetic   C. Chemical   D. Luminous

Ans: B. Magnetic

5. The instrument used to measure electric current is:

A. Voltmeter   B. Galvanometer   C. Ammeter   D. Wattmeter

Ans: C. Ammeter

6. Which of the following is an insulator?

A. Aluminium   B. Iron   C. Plastic   D. Silver

Ans: C. Plastic

7. A fuse is connected in which part of the circuit?

A. Across the battery   B. In series with the appliance   C. In parallel with appliance   D. Across the switch

Ans: B. In series with the appliance

Very Short Answer Questions (1–2 sentences)

Q1: Define electric current.

Ans: Electric current is the flow of electric charge through a conductor, measured in amperes.

Q2: What is a circuit?

Ans: A circuit is a closed path that allows current to flow from the source through components and back.

Q3: Give one example of a conductor.

Ans: Copper is a common conductor used for electrical wiring.

Q4: What does an ammeter measure?

Ans: An ammeter measures the amount of current flowing through a circuit.

Q5: Mention one use of the heating effect.

Ans: Heating effect is used in electric irons and geysers.

Q6: What is an electromagnet?

Ans: An electromagnet is a magnet created by passing current through a wound coil around an iron core.

Q7: Why are insulators used on wires?

Ans: Insulators prevent accidental contact with live wires and protect from electric shocks.

Short Answer Questions (3–5 sentences)

Q1: Explain the heating effect of current with an example.

Ans: When current passes through a conductor, energy is dissipated as heat due to resistance. For example, in an electric heater, the coil becomes hot and transfers heat to the surroundings. This effect is controlled in appliances using proper resistance and fuses.

Q2: Describe how an electromagnet is made and one use.

Ans: An electromagnet is made by winding insulated copper wire into a coil and placing a soft iron core inside; when current flows, the core becomes magnetized. It is used in electric bells and for lifting scrap metal in recycling yards.

Q3: What is the difference between series and parallel circuits?

Ans: In series circuits, components are connected one after another so current is same through all; a break anywhere stops current. In parallel circuits, components share the same voltage independently; one appliance can still work if the other is disconnected.

Q4: How does a fuse protect an electrical appliance?

Ans: A fuse has a thin wire that melts when current exceeds a safe value, breaking the circuit and preventing overheating or fire. It sacrifices itself to save the rest of the circuit.

Q5: What is electroplating?

Ans: Electroplating uses the chemical effect of electric current to deposit a thin layer of metal (like chromium or silver) onto an object to prevent corrosion and improve appearance.

Q6: Why must a voltmeter be connected in parallel?

Ans: A voltmeter measures potential difference between two points, so it must be connected across (in parallel with) the component to measure the voltage correctly without significantly changing the circuit.

Q7: Mention two safety practices while working with electricity at home.

Ans: Always switch off and unplug appliances before cleaning or repairing. Avoid using electrical devices near water and never touch live wires.

Long Answer Questions (Detailed responses)

Q1: Explain the magnetic effect of current and describe a simple experiment to show it.

Ans: Electric current produces a magnetic field around the conductor. To demonstrate, take a long insulated copper wire, connect it to a battery so current flows, and bring a magnetic compass near the wire. You will observe the needle deflecting, showing a magnetic field around the conductor. If the wire is coiled, the magnetic effect becomes stronger and behaves like a magnet when current flows. This is the principle behind electromagnets used in devices such as electric bells and motors.

Q2: Describe in detail the heating effect of electricity and how it is used in everyday appliances including safety considerations.

Ans: When current flows through a conductor, collisions between moving electrons and atoms of the conductor cause energy dissipation as heat. The amount of heat produced depends on current, resistance, and time. Devices like electric irons, geysers, and electric stoves use this effect by choosing materials and wire thickness that produce controlled heating. Safety considerations include the use of proper insulating materials, thermal cut-offs or thermostats to prevent overheating, and fuses to break the circuit in case of excessive current. Using earthing and residual current devices (RCDs) further prevents electric shocks and fire hazards.

Q3: How are series and parallel circuits different in terms of current, voltage, and practical uses? Provide examples of where each is used.

Ans: In series circuits, the same current flows through all components, and the total voltage divides among them. If one component fails, the whole circuit stops. String lights in older homes are an example of series connection (all bulbs go out if one fails). In parallel circuits, each branch receives the full source voltage while the current divides among branches. This is how household wiring is done: lights and appliances get full voltage independently, and one appliance stopping does not affect others. Parallel circuits are preferred for practical domestic and industrial use because of reliability and constant voltage supply.

Q4: Describe the construction and working of an electric bell and explain the role of the magnetic effect of current in it.

Ans: An electric bell consists of an electromagnet, an armature fixed to a hammer, a gong, and a make-and-break switch. When current flows, the electromagnet attracts the armature causing the hammer to strike the gong. The armature movement opens the circuit at the switch, stopping the current; the spring returns the armature to its original position closing the circuit again. This repeating make-and-break action causes the hammer to strike continuously, producing sound. The magnetic effect of current is central: without it the armature would not move and the bell would not work.

Q5: Explain the chemical effect of electric current and describe an important application.

Ans: When current passes through an electrolyte, chemical reactions occur at the electrodes, leading to deposition or dissolution of substances — this is electrolysis. For example, electroplating deposits a metal coating on an object to protect it from corrosion and to enhance appearance. In electroplating, the object to be plated acts as the cathode and metal ions in the solution are reduced at its surface, forming a uniform metal layer. Electroplating is used in jewellery, cutlery, and plating car parts with chromium or nickel.

Q6: How do fuses and MCBs prevent electrical hazards? Compare their working principles and applications.

Ans: A fuse contains a thin wire that melts when excessive current flows, breaking the circuit; it is simple and effective but must be replaced after blowing. An MCB (Miniature Circuit Breaker) otherwise cuts off current automatically through magnetic or thermal action and can be reset without replacement. Fuses are often used in low-cost simple devices, while MCBs are used in modern electrical panels for household and industrial protection because they can be reset quickly and provide better convenience and reliability.

Q7: Discuss environmental and ethical considerations when using electricity and electrical devices.

Ans: Using electricity responsibly helps reduce resource consumption and pollution. Choosing energy-efficient appliances, turning off devices when not in use, and relying on renewable energy sources reduce greenhouse gas emissions from fossil-fuel power plants. Ethically, safe disposal of batteries and electronic waste must be followed to avoid soil and water contamination. Conservation and awareness help ensure electricity access is sustainable for future generations.

Tip: Use this page for revision. Try the MCQs first and then practice writing the short and long answers in your own words.