Electric Current and Its effects Class 7 Worksheet Science Chapter 10

Q.1. True/False
(i) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.

False

• In a battery, cells are connected in series.
• The positive terminal of one cell connects to the negative terminal of the next cell.

(ii) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.

True

The primary role of a fuse is to protect electrical circuits. It does this by:

• Melting and breaking the circuit when the current exceeds a safe limit.
• Preventing overheating of wires, which can lead to fires.
• Ensuring safety by stopping excessive current flow.

Fuses are essential safety devices in electrical systems.

(iii) An electromagnet does not attract a piece of iron.

False

Electromagnets can attract iron and other ferromagnetic materials when an electric current flows through them. Here are some key points:

• Electromagnets become magnets only when current is present.
• They can effectively lift heavy objects.
• When the current is switched off, they lose their magnetism.

(iv) An electric bell has an electromagnet.

True

• An electric bell contains an electromagnet.
• When current flows, the electromagnet attracts a hammer.
• The hammer strikes the bell, producing sound.
• When the circuit breaks, the hammer returns, and the process repeats.

Q.2. Fill in the blanks.
(i) Longer line in the symbol for a cell represents its ____ terminal.

positive
The longer line in the symbol for a cell indicates the positive terminal, while the shorter line represents the negative terminal.

(ii) The combination of two or more cells is called a ____.

battery
A battery is formed when two or more cells are connected together to provide a higher voltage or capacity.

(iii) When current is switched ‘on’ in a room heater, it ____.

produces heat

• When the current is switched on in a room heater, it:
• Produces heat as the electric current flows through the wire.

(iv) The safety device based on the heating effect of electric current is called a ____.

fuse
A fuse is designed to protect electrical circuits by melting and breaking the circuit when excessive current flows, preventing damage or fire.

Q.3. What is electric current?

Electric current is the flow of electrons through a conductor, such as a wire.

• It is measured in amperes.
• Electric current can produce heat when it flows through a wire.
• This heating effect is used in many appliances, like heaters and toasters.
• When current flows, it can also create a magnetic field, making wires behave like magnets.

Q.4. Who discovered magnetic effect of current?

Hans Christian Oersted discovered magnetic effect of current.

Q.5. Which wire used in electric heater and why?

Nichrome wire is used in electric heaters for several reasons:

• It has a high melting temperature, allowing it to withstand high heat without melting.
• Its resistance generates heat efficiently when electric current passes through it.
• It is durable and can maintain its properties over time, making it suitable for repeated heating cycles.

Q.6.  Is it possible for a wire to melt and break? Why?

Yes, a wire can melt and break if a large current flows through it. This occurs due to the following reasons:

• The wire heats up significantly because of the heating effect of electric current.
• If the temperature exceeds the wire's melting point, it can melt and eventually break.
• Wires made from specific materials are designed to melt quickly, which is useful for fuses that protect electrical circuits.

Q.7. Who invented electric bulb?

The credit for the invention of the electric bulb is usually given to Thomas Alva Edison, though others before him had worked on it.

Q.8. Write some uses of battery.

Battery Uses

• Torches for lighting
• Transistors for amplifying signals
• Toys for operation
• TV remote controls for convenience

Q.9. What is filament?

In the bulb there is a thin wire, called the filament, which glows when an electric current passes through it.

Q.10. What is the heating effect of the electric current?

The wire becomes hot when an electric current flows through it. This phenomenon is known as the heating effect of electric current.

• The heat is produced due to the resistance of the wire.
• Different materials and thicknesses of wire affect the amount of heat generated.
• This effect is used in various appliances, such as heaters and toasters.

Q.11. What are the uses of heating effect of electric current?

The heating effect of electric current is utilised in various electrical appliances, including:

• Immersion heaters
• Hotplates
• Irons
• Geysers
• Electric kettles
• Hair dryers

Q.12. Name any two effects of electric current.

The two effects of electric current are:
(i) Heating effect of electric current
(ii) Magnetic effect of the electric current

Q.13. What is an electric circuit?

An electric circuit is a closed path that allows electricity to flow between the two terminals of an electric cell. Key points include:

• The circuit must be closed for current to flow.
• A bulb will only glow when the current is flowing through the circuit.
• If the circuit is open (e.g., when a switch is off), no current flows.

In the bulb, a thin wire called the filament glows when electric current passes through it. If the filament is broken, the circuit becomes incomplete, and the bulb will not glow.

Q.14. Explain the symbol of electric cell.

In the symbol of an electric cell, the representation consists of:

• The longer line indicates the positive terminal.
• The thicker, shorter line represents the negative terminal.

Q.15. Why are fuse wires not used in circuit containing electric cell?

Fuse wires are not used in circuits containing electric cells for the following reasons:

• The current in these circuits is generally low.
• If the circuit breaks, there is minimal risk of fire.

Q.16. Why a fused bulb does not glow?

A fused bulb does not glow due to a break in its filament. This break interrupts the flow of current between the bulb's terminals. As a result:

• The circuit becomes incomplete.
• No current passes through the filament.
• Thus, the bulb remains unlit.

Q.17. Why should we look for ISI mark on electrical appliances?

Before purchasing any electrical appliance, it is important to check for the ISI mark. This mark indicates that:

• The appliance meets safety standards.
• It minimises energy wastage.
• It is reliable and conforms to the specifications set by the Bureau of Indian Standards.

Using products with the ISI mark helps ensure safety and efficiency in electrical appliances.

Q.18. We could not see element in electrical appliances. Give reason.

We cannot see the element in electrical appliances because:

• Elements are typically located inside appliances like immersion heaters, hotplates, irons, geysers, electric kettles, and hair dryers.
• When these appliances are switched on, the elements heat up and become red hot, but they remain hidden from view.

Q.19. Sometimes the cells are placed side by side. Then how are the terminals of the cells connected?

Cells are typically connected using:

• A thick wire or a metal strip that links the positive terminal of one cell to the negative terminal of the next.
• This connection allows the cells to work together as a battery.

Q.20. On what factors does the heat produced in a wire depend?

The amount of heat produced in a wire depends on several factors:

• Material: Different materials conduct electricity differently, affecting heat production.
• Length: Longer wires tend to produce more heat due to increased resistance.
• Thickness: Thicker wires can carry more current with less heat generation.

For various applications, wires of different materials, lengths, and thicknesses are selected to meet specific requirements.