Question: State the observation made by Oersted on the basis of his experiment with current carrying conductors.
Answer: Every current carrying conductor has a magnetic field around it.
Question: State the direction of the magnetic field inside the bar magnet.
Answer: From south to north pole.
Question: Mention the special feature regarding shape of magnetic field lines.
Answer: magnetic field lines are closed curves.
Question: If field lines of a magnetic field are crossed at a point, what does it indicate?
Answer: If field lines of a magnetic field cross each other, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.
Question: What type of core is used to make an electromagnet?
Answer: Soft iron.
Question: Mention the voltage and frequency of current that we receive at our house.
Answer: Voltage: 220 V; Frequency: 50 Hz.
Question: Name the type of current:
- used in household supply,
- given by a cell.
- Alternating current (ac)
- Direct current (dc)
Question: What is the shape of magnetic field lines around a straight current carrying conductor?
Answer: Concentric circles
Question: How can we find the direction of magnetic field due to a straight current carrying conductor?
Answer: By using right hand thumb rule
Question: What is the shape of magnetic field lines around a circular current carrying conductor?
Answer: Straight lines at the center of the conductor
Question: What is a solenoid?
Answer: A cylindrical coil of many tightly would turns of insulated wires with generally diameter of the coil smaller than its length is called a solenoid.
Question: Give the factors on which, magnetic field produced by a current carrying solenoid depends.
Answer: It depends upon:
- the current through the solenoid,
- the number of turns in the solenoid, and
- nature of the core on which the solenoid is would.
Question: Name the rule used to find the direction of force on a current carrying conductor.
Answer: Fleming’s left hand rule
Question: Name the factors on which force acting on a current carrying conductor depends.
Answer: The force depends upon:
- the current through the conductor
- the strength of the magnetic field
- the length of the conductor
Question: What is meant by electromagnetic induction?
Answer: It is the phenomenon of producing electric current in a conductor by changing the magnetic field through the conductor.
Question: State Faraday’s first law of electromagnetic induction.
Answer: Whenever magnetic field through a coil is changed, an emf is produced in the coil. The emf last as long as the magnetic field through the coil changes.
Question: State Faraday’s second law of electromagnetic induction.
Answer: The induced emf depends directly upon the relative speed between the coil and the magnet.
Question: State the rule which you use to find the direction of induced current or state Fleming’s right hand rule.
Answer: It states “Stretch the forefinger, the middle finger and the thumb of your right hand mutually perpendicular to each other, then if the thumb represents the direction of force, forefinger represents the direction of magnetic field, then the middle finger represents the direction of current.”
Question: How is alternating current different from direct current?
Answer: Alternating current changes in magnitude and its direction reverses periodically whereas direct current’s magnitude and direction remain same.
Question: Name three colors used and names of the used in household wiring.
Answer: Red, black and green (Old convention) and Brown, blue and green (New convention).
Question: Name two types of writing system adopted for domestic wiring.
Answer: The tree system and the ring system.
Question: Why is earthing important for electrical appliance?
Answer: It safes the person operating the device from electric shock and also saves the device from excessive currents due to some fault.
Question: What colour wire is used for earthing or grounding?
Answer: Green of yellow.
Question: How can it be shown that a magnetic field exists around a wire through which a direct current is passing?
Answer: We will place a compass needle near the wire carrying current. If this needle gets deflected, it will show that there is a magnetic field around the wire.
Question: How is the strength of the magnetic field at a point near a wire related to the strength of the electric current flowing in the wire?
Answer: The strength (B) of the magnetic field at a point near a wire is directly proportional to the strength (I) of the current flowing in the wire.
Question: An alternating electric current has a frequency of 50 Hz. How many times does it change its direction in one second?
Answer: Since ac changes its direction twice in a cycle, it will change its direction 100 times (= 50 × 2) in 1 second as its frequency is 50 Hz.
Question: What will be the frequency of an alternating current if it direction change after every 0.01s?
Answer: Since ac changes its direction after every 0.01 s, it completes one cycle (i.e., changes its direction twice) in 2 × 0.01 = 0.02 s. Obviously, it completes 50 cycles in 1 second. Therefore, its frequency is 50 Hz.
Question: What is short-circuiting in an electric supply?
Answer: Short-circuiting in an electric circuit is a situation in which the live wire touches the neutral wire.
Question: What is constitutes the field of a magnet?
Answer: The space around a magnet within which its magnetic effect can be experienced constitutes the magnetic field of the magnet.
Question: What is the advantage of the third wire of earth connection in domestic appliances?
Answer: In case of a defect in any domestic appliance, current leaks to its body. The third wire of earth connection transfers this current to the earth. As a result of this, the user of the appliance is protected from the electric shock.
Question: How can you show that the magnetic field produced by a given electric current in the wire decrease as the distance from the wire decreases?
Answer: If we take a magnetic compass slowly away from the current carrying conductor, the deflection of the compass decreases. This shows that the magnetic field decrease as move away from the current carrying conductor.
Question: What is the shape of the magnetic field lines inside a solenoid?
Answer: The magnetic field lines inside a solenoid are in the form of parallel straight lines.
Question: How can you magnetize a piece of magnetic material?
Answer: We can do so by placing it inside a current carrying solenoid.
Question: Why is the metallic body of electrical devices connected to the earth wire?
Answer: This is because it provides a low resistance conducting path for the current to flow to the earth, thereby protecting the user from a severe electric shock.
Question: How is a circuit overloaded?
Answer: It is overload by connecting too many devices to it.
Question: What is short-circuiting?
Answer: The coming together of the live and the neutral wire is called short-circuiting.
Question: What is the function of a field magnet in an ac generator?
Answer: It produces the magnetic field in which the coil of the generator moves.
Question: What is the frequency of dc?