CBSE Class 10 Science HOTs Magnetic Effects of Electric Current Set 04

Force on a Current-Carrying Conductor in a Magnetic Field

Question. Which one of the following would not experience a force while moving perpendicular to a uniform magnetic field?
(a) A neutron
(b) An alpha particle
(c) An electron
(d) A proton
Answer: (a) A neutron

Question. The direction of force acting on current carrying conductor in external magnetic field is given by
(a) right hand thumb rule
(b) Fleming’s left hand rule
(c) Fleming’s right hand rule
(d) Maxwell’s cork screw rule
Answer: (b) Fleming’s left hand rule

Question. When current is parallel to magnetic field, then force experience by the current carrying conductor placed in uniform magnetic field is
(a) twice to that when angle is \( 60^\circ \)
(b) thrice to that when angle is \( 60^\circ \)
(c) zero
(d) infinite
Answer: (c) If the current direction is parallel to the magnetic field, then there will no force on the conductor exerted by the magnetic field.

Question. Which of the following factors affect the strength of force experience by a current carrying conduct in a uniform magnetic field?
(a) Magnetic field strength
(b) Magnitude of current in a conductor
(c) Length of the conductor within magnetic field
(d) All of the options
Answer: (d) All of the options

Question. A positive charge is moving upwards in a magnetic field directed towards north. The particle will be deflected towards
(a) west
(b) north
(c) south
(d) east
Answer: (a) west

Question. The force acting on conductor is directly proportional to
(a) strength of external field
(b) strength of electric current
(c) length of conductor
(d) All of the options
Answer: (d) All of the options

Question. The maximum force is exerted on the conductor when angle between its direction and that of magnetic field is
(a) \( 0^\circ \)
(b) \( 45^\circ \)
(c) \( 90^\circ \)
(d) \( 180^\circ \)
Answer: (c) \( 90^\circ \)

Question. A device based on principle of force acting on a current carrying conductor in external magnetic field is
(a) electric motor
(b) electric generator
(c) fuse wire
(d) earth wire
Answer: (a) electric motor

Question. A current carrying wire has no tendency to rotate in a magnetic field what does it mean?
(a) wire is parallel to direction of magnetic field.
(b) wire is perpendicular to direction of magnetic field.
(c) wire is having very strong current flowing through it.
(d) magnetic field is very strong.
Answer: (a) wire is parallel to direction of magnetic field.

Question. (a) An alpha particle while passing through a magnetic field gets projected towards north. In which direction will an electron project when it passes through the same magnetic field? (b) Name the rule to determine the direction of magnetic field and direction of motion of electron.
Answer: (a) South (b) In both cases it is Fleming’s Left Hand rule.

Question. When is the force experienced by a current carrying straight conductor placed in uniform magnetic field (a) Maximum; (b) Minimum 
Answer: (a) Maximum: When the direction of current in a current carrying conductor is perpendicular to the direction of magnetic field. (b) Minimum: (Zero) When the direction of current in a current carrying conductor is parallel/anti-parallel/along the direction of magnetic field.

Question. What are the factors which govern the force experienced by a current carrying conductor placed in a uniform magnetic field depends?
Answer: The factors which govern the force experienced by conductor which is placed in a uniform magnetic field are: (a) strength of the magnetic field in which conductor is placed. (b) strength of current flowing through the conductor. (c) length of conductor.

Question. Why and when does a current carrying conductor kept in a magnetic field experience force? List the factors on which direction of this force depends? 
Answer: The drifting of free electrons of a conductor in a definite direction causes the current to flow through it. When such conductor is placed in a uniform magnetic field, each drifted electron of a conductor experience a magnetic force. This force is collectively experience by a conductor as a whole. Hence a current carrying conductor kept in a magnetic field experience a force. The direction of magnetic force depends on (i) direction of current through the conductor, and (ii) direction of magnetic field.

Question. What happens to the force acting on current carrying conductor placed in magnetic field when: (a) Direction of magnetic field is reversed without changing the direction of current. (b) Direction of the current is reversed without changing the direction of magnetic field. (c) Direction of both the current and the magnetic field is reversed.
Answer: Force acting on a current carrying conductor placed in a magnetic field will (a) act in opposite direction to that of previous direction. (b) act in opposite direction to that of previous direction. (c) remain in the same direction.

Question. (a) Mention the factors on which the direction of force experienced by a current carrying conductor placed in a magnetic field depend. (b) A proton beam is moving along the direction of magnetic field. What force acting on proton beam? (c) The diagram shows a beam of electrons about to enter a magnetic field. The direction of the field is into the page. [HOTS] What will be the direction of deflection, if any, as the beam passes through the field?
Answer: (a) The direction of force experienced by a current carrying conductor placed in a magnetic field depends on (i) direction of current in a conductor, and (ii) direction of magnetic field. (iii) angle between the direction of current and direction of magnetic field and (iv) length of the conductor which is placed in magnetic field. (b) The parallel or anti-parallel magnetic field does not exert any force on the charge particle which moves along the direction of magnetic field. Hence, the proton beam does not experience any force. (c) Direction of current is from right to left as electron beam enters from left to right and magnetic field is into the page. So, according to Fleming’s left hand rule, force is perpendicular to the flow of current and in its left side. So, electron beam deflects towards bottom of the page.

QUESTIONS

Question. Magnitude of the magnetic force experienced by a current carrying conductor in a uniform magnetic field is maximum when the magnetic field and current direction are
(a) mutually perpendicular to each other
(b) at angle of \( 60^\circ \)
(c) at angle of \( 120^\circ \)
(d) at angle of \( 180^\circ \)
Answer: (a) mutually perpendicular to each other

Question. The current in the wire is directed towards east and wire is placed in a magnetic field towards north, the force on the wire is
(a) due east
(b) due west
(c) vertically downwards
(d) vertically upwards
Answer: (d) vertically upwards

Question. Name two devices that uses the current carrying conductors and magnetic field.
Answer: Electric motor and loudspeakers.

Question. State whether an alpha particle will experience any force in a magnetic field if (alpha particles are positively charged particles) (a) it is placed in the field at rest. (b) it moves in the magnetic field parallel to field lines. (c) it moves in a magnetic field perpendicular to field lines. Justify your answer in each case. 
Answer: (a) No, as force \( F = qvB \sin\theta \). If \( v = 0 \), \( F = 0 \). (b) No, as \( \theta = 0^\circ \), \( \sin 0^\circ = 0 \), hence \( F = 0 \). (c) Yes, force is maximum as \( \theta = 90^\circ \), \( \sin 90^\circ = 1 \), hence \( F = qvB \).

Domestic Electric Circuits

Question. At the time of short circuit, the electric current in the circuit 
(a) vary continuously
(b) does not change
(c) reduces substantially
(d) increases heavily
Answer: (d) increases heavily

Question. The most important safety method used for protecting home appliances from short circuiting or overloading is
(a) earthing
(b) use of fuse
(c) use of stabilizers
(d) use of electric meter
Answer: (b) use of fuse

Question. Earth wire carries
(a) current
(b) voltage
(c) no current
(d) heat
Answer: (c) no current

Question. Which among of these are the main characteristics of fuse element?
(a) High conductivity
(b) Low melting point
(c) Do not burn due to oxidation
(d) All of the options
Answer: (d) All of the options

Question. Overloading is due to
(a) Insulation of wire is damaged
(b) Fault in the appliances
(c) Accidental hike in supply voltage
(d) All of the options
Answer: (d) All of the options

Question. The metallic body of electrical appliances are connected to the earth wire. For the current, this will provide
(a) a low-resistance conducting path.
(b) a high-resistance insulating path.
(c) a medium resistance conducting path.
(d) a closed zero resistance insulating path.
Answer: (a) a low-resistance conducting path.

Question. The potential difference between the live wire and neutral wire in our country is
(a) 110 V
(b) 220 V
(c) 300 V
(d) 50 V
Answer: (b) 220 V

Question. The user of electrical appliances may not get a severe electric shock due to
(a) touching the appliances with bare foot
(b) absence of fuse wire
(c) earthing of appliances
(d) short circuit
Answer: (c) earthing of appliances

Question. Which type of current rating supply is required in our country for the electrical devices such as geysers, air conditioners, room heaters etc?
(a) 220 V, 5 A
(b) 110 V, 5 A
(c) 220 V, 15 A
(d) 110 V, 15 A
Answer: (c) 220 V, 15 A

Question. In domestic electric circuits the wiring with 15 A current rating is for the electric devices which have 
(a) higher power ratings such as geyser.
(b) lower power ratings such as fan.
(c) metallic bodies and low power ratings.
(d) non-metallic bodies and low power ratings.
Answer: (a) higher power ratings such as geyser.

Question. Give scientific reasons. (a) Wires carrying electricity should not be touched when bare-footed. (b) We must not use many electrical appliances simultaneously.
Answer: (a) When we touch the live wire bare-footed, our body is directly in contact with the earth. So, current passes through the body to the earth. As our body is good conductor of electricity, we get a severe shock. Hence, we should not handle live wires bare footed. (b) When many high power rating appliances are switched on simultaneously, a large amount of current flows through the main circuit and current may exceed the bearing capacity of the connecting wires. This causes overloading, which may cause fire. Hence, we must not use many electrical simultaneously.

Question. Explain, why fuse wire is made of a tin-lead alloy and not copper?
Answer: Tin-lead alloy has a low melting point so wire made of this alloy melt easily whereas copper has a high melting point due to which fuse made of copper wire will not melt easily when a short circuit takes place.

Question. Explain any two situations that can cause electrical hazards in domestic circuits. 
Answer: (i) Connecting too many electrical devices to a single socket or in the extension cord for any length of time draws high current from the mains that will exceed the current rating of connecting wires. The wires cannot withstand such a high current and melt and may cause fire. (ii) Most electrical hazards in domestic circuits are caused by the faulty electrical outlets, old and out-dated appliances. The chances of short circuit, i.e. contact of live wire and neutral wires with each other due to damage in their insulation or some fault in the appliances are very high. It may result spark at the contact point which may even cause fire.

Question. (a) Electrical switches should not be operated with wet hand. (b) In domestic electric circuit, with which wire we connect a fuse?
Answer: (a) Switches should not be operated with wet hand: Water is a good conductor of electricity as it contains salt and impurities. When we touch the switch with wet hand, it is possible that electric current will pass through our body and we get a severe shock. (b) Fuse is always connected in series with live wire.

Question. Earth wire has zero voltage just like the neutral wire, then what is the difference between these two wires?
Answer: Earth wire provides a good grounding connection between the metallic case of an electrical appliance and the ground, which helps to save the user from getting a severe electric shock in case of any leakage of current, while neutral wire provides a return path for the current.

Question. Cable of a microwave oven has three wires inside it which have insulation of different colours black, green and red. Mention the significance of the three colours and potential difference between red and black one. 
Answer: Significance of insulation colour: (i) Red colour insulation wire – Live wire (ii) Black colour insulation wire – Neutral wire (iii) Green colour insulation wire – Earth wire. Live wire is at higher potential of 220 V while neutral wire is at zero potential. So, potential difference between red and black insulation wire is 220 V.

Question. (a) Why switches are connected in live wire not in neutral wire? (b) Can we use the same kind of fuse for both power and lightning circuits?
Answer: (a) Switch is always connected in the live wire because (i) the appliances must be put to the high potential terminal. (ii) in OFF position, circuit is incomplete, i.e. the circuit will becomes an open circuit. Therefore, no current reaches to appliances. But if we connect the switch in neutral wire, the appliance remain connected with live wire which is dangerous for the user. (b) No, for power circuit, the fuse rating is 15 A while for lightning circuit, fuse rating is 5 A.

Question. (i) Why is an alternating current (A.C.) considered to be advantageous over direct current (D.C.) for the long distance transmission of electric power? (ii) How is the type of current used in household supply different from the one given by a battery of dry cells? (iii) How does an electric fuse prevent the electric circuit and the appliances from a possible damage due to short circuiting or overloading? 
Answer: (i) AC is preferred over DC because it can be transmitted over long distance without much loss of energy. (ii) In household supply, alternating current (AC) is used. The source of AC is AC generator. The current given by a battery of dry cell is direct current (DC). (a) The alternating current (AC) reverses its direction periodically whereas the direct current (DC) always flow in one direction. (b) The frequency of AC is 50 Hz while that for DC is zero. (iii) Fuse wire, an alloy of copper, aluminium, tin, lead, etc. having low melting point. When excessive amount of current larger than the specified value due to short circuiting or overloading flows through the circuit, the temperature of fuse wire increases. The heating effect of current causes the fuse wire to melt and breaks the circuit there by stopping the flow of current in the circuit. Thus, electric fuse prevent the electric circuit and appliances from a possible damage due to short circuiting or overloading.

Question. State the consequences that can lead to a short circuit. Or One of the major cause of fire in office building is short circuiting. List three factors which may lead to the short circuit. 
Answer: It occurs as a consequence of: failure of electrical insulations due to which live wire comes in direct contact with neutral or earth wire; presence of external conducting material (such as water) that is introduced accidently into the circuit; electrical appliances are forced to operate when its moving parts are jammed; connection of current carrying parts of electrical equipment’s to one another due to human or natural cause or use of less rating wires. When this happens, there is a flow of an excessive electric current which can damage the circuit and may also cause electrical fires.

Question. Explain the meaning of overloading of an electrical circuit. List two possible causes due to which overloading may occur in household circuits. Write one preventive measure that should be taken to avoid overloading of domestic circuits. 
Answer: Overloading: If the current drawn by the many electrical appliances connected to a single socket exceeds the current rating of the wire, the entire circuit or part of circuit gets heated and can even cause fire. This is known as overloading. It might be due to (i) accidental hike in supplied voltage or (ii) connecting too many appliances to a single socket or (iii) damage in the insulation of wires or (iv) some fault in the appliances or (v) direct contact between a live wire and a neutral wire. Preventive measure to avoid overloading are: (i) An excess number of electrical device should not be connected to the same single socket. (ii) One should not use too many appliances having high power device at the same time.