Quick Review Flashcards - Click to flip and test your knowledge!
Question
Which scientist discovered the link between electricity and magnetism in 1820?
Answer
Hans Christian Oersted discovered this connection.
Question
What phenomenon occurs when an electric current flowing through a conductor produces a magnetic field around it?
Answer
This is known as the magnetic effect of electric current.
Question
The region around a magnet or a current-carrying wire where its magnetic effect can be felt is called a _____.
Answer
magnetic field
Question
How does a magnetic compass needle behave when placed near a wire carrying an electric current?
Answer
The needle gets deflected from its original direction.
Question
What happens to the magnetic field around a wire when the electric current stops flowing?
Answer
The magnetic field disappears.
Question
Term: Electromagnet
Answer
Definition: A current-carrying coil of wire that behaves as a magnet.
Question
Why is an iron core typically inserted into the coil of an electromagnet?
Answer
The iron core makes the electromagnet stronger.
Question
What happens to the iron paper clips held by an electromagnet when the circuit is opened?
Answer
The magnetic field disappears and the clips fall off.
Question
How can the polarity (North and South poles) of an electromagnet be reversed?
Answer
The polarity is reversed by changing the direction of the electric current.
Question
If the North pole of a magnetic compass is attracted to 'End A' of an electromagnet, what is the polarity of 'End A'?
Answer
End A is the South pole.
Question
How does increasing the number of turns in a coil affect the strength of an electromagnet?
Answer
Increasing the number of turns makes the electromagnet stronger.
Question
How does increasing the magnitude of the electric current affect the magnetic field of a coil?
Answer
A larger current creates a stronger magnetic field.
Question
Name two practical applications for the magnetic effect of electric current mentioned in the text.
Answer
Practical applications include electric bells and loudspeakers.
Question
Where are lifting electromagnets commonly used to move heavy metal items efficiently?
Answer
They are used in factories and scrap yards.
Question
What movement deep inside the Earth's core creates the electric currents that generate its magnetic field?
Answer
The movement of liquid iron creates these currents.
Question
How does the Earth's magnetic field help protect life on Earth?
Answer
It acts as a shield that blocks harmful particles from space.
Question
Which animals are mentioned as using the Earth's magnetic field to navigate across continents and oceans?
Answer
Migratory birds, fish, and animals use the field for navigation.
Question
What is the name of the phenomenon where a conductor gets heated as electric current passes through it?
Answer
This is known as the heating effect of electric current.
Question
Why does a conductor produce heat when an electric current flows through it?
Answer
Heat is produced because the conductor offers resistance to the flow of current.
Question
How does the resistance of nichrome wire compare to copper wire of the same size and length?
Answer
Nichrome wire offers higher resistance than copper wire.
Question
What four factors determine the amount of heat generated in a wire by an electric current?
Answer
Heat depends on the wire's material, thickness, length, and the duration of current flow.
Question
Term: Heating element
Answer
Definition: A rod or coil of wire in an appliance that converts electrical energy into heat energy.
Question
Name three household appliances that work on the principle of the heating effect of electric current.
Answer
Appliances include electric room heaters, irons, and kettles.
Question
What happens to the heating element of a room heater when it is switched on?
Answer
The heating element can be seen glowing red hot.
Question
Why does an incandescent lamp glow when connected to a circuit?
Answer
The lamp glows because its filament is heated by the electric current.
Question
What is a potential safety hazard of overheating in household electrical circuits?
Answer
Overheating can melt plastic parts in plugs and sockets or lead to fires.
Question
How can unnecessary heating in household switchboards be prevented?
Answer
Use appropriate wires, plugs, and sockets rated for the specified electric current.
Question
In Sumana's model, what replaced the hook of a typical crane to lift paper clips?
Answer
An iron nail wrapped with wire connected to a battery was used.
Question
What is the effect of using a battery with more cells on the deflection of a compass needle in an electromagnet circuit?
Answer
A battery with more cells increases the deflection of the needle.
Question
According to the 'Safety First' advice, why should you not connect wires to a cell for an extended period?
Answer
Connecting wires for too long may weaken the cell quickly.
Question
What is the thickness of the nichrome wire used in Activity 4.5 to observe the heating effect?
Answer
The wire has a thickness of about $0.3\text{ mm}$ ($26\text{--}28$ gauge).
Question
In Activity 4.3, what was the purpose of rolling chart paper into a cylinder?
Answer
The paper cylinder served as a base to wind the insulated wire into a coil.
Question
Why does a freely suspended magnet rest along the North-South direction?
Answer
It aligns this way because the Earth itself behaves like a giant magnet.
Question
Cloze: The magnetic field produced by a current-carrying coil disappears when the current _____.
Answer
stops flowing
Question
What is the primary difference in heat generation when using a battery of two cells versus a single cell in the same circuit?
Answer
A two-cell battery generates more heat because the current magnitude is higher.
Question
Which specific device is mentioned as being used to make a switch in Activity 4.1?
Answer
A safety pin is used to make the switch.
Question
How does the crane operator control a lifting electromagnet?
Answer
The operator controls it by switching the electric current ON and OFF.
Question
What did Mohini and Aakarsh learn about magnetic materials in Grade 6?
Answer
They learned that magnetic materials like iron are attracted by magnets.
Question
Which instrument is used to determine if a current-carrying wire is producing a magnetic field?
Answer
A magnetic compass is used to detect the field.
Question
True or False: All conductors offer the same level of resistance to the flow of electric current.
Answer
False; different conductors offer different levels of resistance.
Question
Process: Making an electromagnet
Answer
Step: Tightly wrap an insulated wire around an iron nail and connect the ends to an electric cell.
Question
What is the role of 'safety devices' in household circuits?
Answer
They are placed in the circuit to minimise incidents such as fires from overheating.
Question
According to Activity 4.4, if the South pole of a compass is attracted to 'End B', what is the polarity of 'End B'?
Answer
End B is the North pole.
Question
What happens to the magnetic compass needle when the switch is moved to the 'OFF' position in Activity 4.1?
Answer
The needle returns to its original direction.
Question
Cloze: A current-carrying coil with an iron core behaves as a _____ magnet.
Answer
stronger
Question
What is the relationship between electricity and magnetism according to Hans Christian Oersted's discovery?
Answer
Electricity and magnetism are linked; electric current produces a magnetic field.
Question
Identify the component: A flexible insulated wire wrapped in the form of a coil.
Answer
This component is an electromagnet coil.
Question
In the context of electrical appliances, what is converted into heat energy due to resistance?
Answer
Electrical energy is converted into heat energy.
Question
What determines the magnitude of heat produced in a heating element?
Answer
The magnitude of the electric current flowing through the element determines the heat.
Question
How can you experimentally confirm that an electromagnet has two poles?
Answer
By placing a magnetic compass at each end and observing which pole is attracted.
Question
What is the effect of changing the direction of current on the magnetic field of an electromagnet?
Answer
Changing the current direction reverses the magnetic poles.
Question
What is the approximate length of the nichrome wire used in Activity 4.5?
Answer
The wire is approximately $10\text{ cm}$ in length.
Question
Besides magnets, what else can cause the deflection of a compass needle?
Answer
A current-carrying wire can also cause the deflection.
Question
In lifting electromagnets, what state must the current be in to release a load of scrap metal?
Answer
The current must be switched OFF.
Question
Which Grade 7 chapter is referenced for making a switch for Activity 4.1?
Answer
The chapter 'Electricity: Circuits and their Components' is referenced.
Question
How does the duration for which current flows affect the heat generated in a conductor?
Answer
The longer the current flows, the more heat is generated.
Question
What kind of core do most practical electromagnets use?
Answer
Most practical electromagnets use an iron core.
Question
Cloze: The Earth's magnetic field acts as a _____ against harmful particles from space.
Answer
shield
Question
What happens to the magnetic field of an electromagnet when the electric cell is disconnected?
Answer
The magnetic field disappears immediately.
Question
Atomic Question: Does the nichrome wire in Activity 4.5 feel warm before the switch is turned ON?
Answer
No, it only feels warm after current is passed through it.