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Q1. An electric generator converts:
An electric generator converts mechanical energy into electrical energy. When a coil rotates in a magnetic field, the magnetic flux through the coil changes, inducing an electric current. This is based on the principle of electromagnetic induction discovered by Faraday.
Q2. The split ring in an electric motor acts as a:
The split ring in an electric motor acts as a commutator. Its function is to reverse the direction of current in the coil every half rotation, ensuring that the torque on the coil always acts in the same direction, allowing continuous rotation.
Q3. A solenoid behaves like a:
A solenoid behaves like a bar magnet when current flows through it. One end of the solenoid acts as a north pole and the other as a south pole. The magnetic field inside a solenoid is uniform and parallel, similar to that of a bar magnet.
Q4. Materials that offer very low resistance to electric current are called:
Materials that offer very low resistance to electric current are called conductors. Examples include copper, aluminium, and silver. They have a large number of free electrons that can move easily, allowing current to flow with minimal opposition.
Q5. An induced current exists only when there is:
An induced current exists only when there is a changing magnetic field. A steady magnetic field does not induce any current. The change in magnetic flux through a coil is essential for electromagnetic induction.
Q6. The force on a current-carrying conductor placed in a magnetic field is maximum when the conductor is:
The force on a current-carrying conductor is maximum when the conductor is perpendicular (at right angles) to the magnetic field. The force is given by F = BIL sin θ, and sin 90° = 1, giving the maximum force.
Q7. An AC generator produces current that:
An AC generator produces alternating current (AC) that changes direction periodically. As the coil rotates in the magnetic field, the induced current reverses direction every half rotation. This periodic reversal is the defining characteristic of AC.
Q8. The magnetic field at the centre of a long circular coil carrying current consists of:
The magnetic field at the centre of a long circular coil (or solenoid) consists of parallel straight lines. This indicates that the magnetic field is uniform at the centre. The field lines are equally spaced and have the same direction.
Q9. An electric short circuit occurs when:
An electric short circuit occurs when the live wire and the neutral wire touch directly (or come into contact through a low-resistance path). This bypasses the appliances and causes a very large current to flow, which can damage the circuit and cause fire.
Q10. When a bar magnet is pushed into a coil connected to a galvanometer, the galvanometer shows:
When a bar magnet is pushed into a coil connected to a galvanometer, the galvanometer shows a momentary deflection. The induced current exists only while the magnet is moving (changing magnetic flux). Once the magnet stops, the deflection returns to zero.
Q11. A DC generator uses which device to obtain unidirectional current?
A DC generator uses a split-ring commutator to obtain unidirectional current. The commutator reverses the connection of the coil to the external circuit every half rotation, ensuring that the current always flows in the same direction.
Q12. An electric generator works on the principle of:
An electric generator works on the principle of electromagnetic induction. When a coil rotates in a magnetic field, the changing magnetic flux induces an electric current in the coil. This converts mechanical energy into electrical energy.
Q13. The unit of capacitance is:
The unit of capacitance is the farad (F). It is named after the English scientist Michael Faraday. One farad is the capacitance of a capacitor that stores one coulomb of charge when a potential difference of one volt is applied across it.
Q14. An electron beam moving forward is deflected to the right. The magnetic field is directed:
Using Fleming’s left-hand rule (or the rule for a moving charge in a magnetic field), if an electron beam moving forward is deflected to the right, the magnetic field is directed downwards. The force on a moving charge is given by F = q(v × B).
Q15. Electric power is transmitted over long distances using AC because:
Electric power is transmitted over long distances using AC because it can be transmitted with less energy loss. AC voltage can be stepped up using transformers, which reduces current and hence reduces power losses (I²R losses) during transmission.
Q16. Voltage is also known as:
Voltage is also known as potential difference. It is the work done per unit charge to move a charge between two points. The SI unit of voltage is the volt (V). Voltage is what drives electric current through a circuit.
Q17. Increasing the number of turns in a coil increases the:
Increasing the number of turns in a coil increases the magnetic field strength. The magnetic field of a solenoid is directly proportional to the number of turns per unit length (B ∝ n). More turns mean a stronger magnetic field.
Q18. A fuse wire should have:
A fuse wire should have a low melting point so that it melts easily when excess current flows. This breaks the circuit and protects appliances. The fuse wire is made of an alloy with a low melting point, such as tin-lead alloy.
Q19. The SI unit of electric current is:
The SI unit of electric current is the ampere (A). One ampere is defined as the flow of one coulomb of charge per second. It is named after the French physicist André-Marie Ampère.
Q20. A transformer is a device used to:
A transformer is a device used to change (step up or step down) the voltage of alternating current (AC). It works on the principle of mutual induction. Transformers are essential for efficient transmission of electrical power over long distances.
Q21. An electric motor converts:
An electric motor converts electrical energy into mechanical energy. The current-carrying coil experiences a force in a magnetic field, causing it to rotate. This rotation can be used to do mechanical work, such as turning a fan or a wheel.
Q22. The magnetic field inside a solenoid is:
The magnetic field inside a solenoid is uniform. The field lines are parallel and equally spaced, indicating that the field has the same strength and direction at all points inside the solenoid. This is one of the key properties of a solenoid.
Q23. The role of neutral wire in domestic circuits is to:
The role of the neutral wire in domestic circuits is to complete the circuit. It carries the return current from the appliance back to the source. The neutral wire is at zero potential with respect to the earth and provides the return path for current.
Q24. The rule used to find the direction of induced current in a rotating coil is:
Fleming’s right-hand rule is used to find the direction of induced current in a rotating coil (or any conductor moving in a magnetic field). The thumb points in the direction of motion, the forefinger in the direction of the magnetic field, and the middle finger gives the direction of induced current.
Q25. The axle in an electric motor helps to:
The axle in an electric motor helps to rotate the coil. The axle is connected to the rotating coil and transmits the mechanical energy (rotation) to the outside, allowing the motor to do useful work.
Q26. The magnetic field is strongest where field lines are:
The magnetic field is strongest where field lines are closely spaced. The density of field lines indicates the strength of the magnetic field. Closer lines mean a stronger field, which is why the field is strongest at the poles of a magnet.
Q27. A wire with green insulation in domestic wiring is the:
A wire with green insulation (or green with yellow stripes) in domestic wiring is the earth wire. It provides a safety path for leakage current to flow to the ground, protecting users from electric shocks.
Q28. Fleming’s left-hand rule is used to determine the direction of:
Fleming’s left-hand rule is used to determine the direction of the force on a current-carrying conductor placed in a magnetic field. The thumb gives the direction of force, the forefinger gives the magnetic field direction, and the middle finger gives the current direction.
Q29. When a bar magnet is held stationary inside a coil, the galvanometer shows:
When a bar magnet is held stationary inside a coil, there is no change in magnetic flux through the coil. Therefore, no current is induced, and the galvanometer shows no deflection. Electromagnetic induction requires a changing magnetic field.
Q30. The scattering of light by colloidal particles is called:
The scattering of light by colloidal particles is called the Tyndall effect. When a beam of light passes through a colloidal solution, the particles scatter the light, making the path of the beam visible. This effect is named after John Tyndall.
Q31. AC supply in India has a frequency of:
AC supply in India has a frequency of 50 Hz. This means the current changes direction 100 times per second (50 complete cycles per second). In the USA and some other countries, the frequency is 60 Hz.
Q32. A galvanometer is mainly used to detect:
A galvanometer is mainly used to detect the presence and direction of electric current. It is a sensitive instrument that deflects when current flows through it. The amount of deflection indicates the strength of the current.
Q33. Current is induced in coil B when current in nearby coil A changes because of:
Current is induced in coil B when the current in nearby coil A changes because of the changing magnetic field. The changing current in coil A produces a changing magnetic field, which induces a current in coil B. This is called mutual induction.
Q34. An ammeter is used to measure:
An ammeter is used to measure electric current flowing through a circuit. It is always connected in series with the circuit so that the entire current passes through it. The unit of measurement is amperes (A).
Q35. Which of the following devices uses an electric motor?
An electric fan uses an electric motor to convert electrical energy into mechanical energy, which rotates the fan blades. Electric bulbs produce light, fuses are safety devices, and voltmeters measure voltage.
Q36. The earth wire is necessary in domestic appliances to:
The earth wire is necessary in domestic appliances to prevent electric shock. If the metallic body of an appliance becomes live due to a fault, the earth wire provides a low-resistance path for the current to flow to the ground, protecting the user.
Q37. The direction of magnetic field is given by the direction in which the north pole of a compass moves:
The direction of the magnetic field is given by the direction in which the north pole of a compass moves. This is the standard convention for defining the direction of magnetic field lines—they always point from the north pole to the south pole outside the magnet.
Q38. The magnetic field around a straight current-carrying wire consists of:
The magnetic field around a straight current-carrying wire consists of concentric circles centred on the wire. The circles are in a plane perpendicular to the wire, and the direction is given by the right-hand thumb rule.
Q39. Magnetic field lines never intersect because:
Magnetic field lines never intersect because if they did, the magnetic field would have two different directions at the point of intersection, which is impossible. The magnetic field has a unique direction at each point.
Q40. Brushes in an electric generator are used to:
Brushes in an electric generator are used to collect current from the rotating coil (via slip rings or commutator) and deliver it to the external circuit. The brushes are stationary and press against the rotating rings.
Q41. Materials that do not allow electric current to flow are called:
Materials that do not allow electric current to flow are called insulators. Examples include rubber, glass, and plastic. Insulators have very high resistivity and are used to prevent electric shock by covering wires.
Q42. A soft iron core is used in electromagnets because it:
A soft iron core is used in electromagnets because it gets magnetised easily and loses its magnetism quickly when the current stops. This makes it ideal for electromagnets, which need to be turned on and off.
Q43. Which of the following is NOT a source of magnetic field?
An electric insulator is NOT a source of a magnetic field. Current-carrying conductors, solenoids, and bar magnets all produce magnetic fields. Insulators do not conduct current and do not produce magnetic fields.
Q44. One ohm is defined as the resistance when:
One ohm is defined as the resistance when a potential difference of 1 volt produces a current of 1 ampere. This is based on Ohm’s law: R = V/I. So, 1 Ω = 1 V / 1 A.
Q45. A current-carrying conductor placed in a magnetic field experiences a force because of interaction between:
A current-carrying conductor placed in a magnetic field experiences a force because of the interaction between the magnetic field produced by the current and the external magnetic field. This force is given by F = BIL sin θ.
Q46. The study of electricity and magnetism together is called:
The study of electricity and magnetism together is called electromagnetism. It deals with the relationship between electric and magnetic fields, including the magnetic effects of electric current and the electric effects of moving magnets.
Q47. The rule used to find the direction of magnetic field around a straight current-carrying conductor is:
The right-hand thumb rule is used to find the direction of the magnetic field around a straight current-carrying conductor. If the thumb points in the direction of current, the curled fingers give the direction of the magnetic field lines.
Q48. A device that converts electrical energy into sound energy is:
A loudspeaker converts electrical energy into sound energy. It works on the magnetic effect of current—a current-carrying coil vibrates in a magnetic field, producing sound waves. Generators produce electricity, motors produce mechanical energy, and transformers change voltage.
Q49. The phenomenon used in generators is discovered by:
The phenomenon used in generators (electromagnetic induction) was discovered by Michael Faraday in 1831. He found that a changing magnetic field induces an electric current in a conductor. This is the principle behind electric generators.
Q50. The direction of conventional current is taken as:
The direction of conventional current is taken as opposite to the flow of electrons. Electrons flow from negative to positive, but conventional current is assumed to flow from positive to negative. This convention was established before the discovery of electrons.