CBSE Class 10 Science Magnetic Effects Of Current Worksheet Set B

Question. An alternating electric current has a frequency of 50 Hz. How many times does it change its direction in one second? Give reason for your answer.
Answer : 100 times in one second because one complete cycle involves two times change of direction.

Question. Identify the type of magnetic fields represented by the magnetic field fines given below and name the type conductors which can produce them.

Answer : a. Magnetic field lines of a current carrying circular loop.
b. Magnetic field lines in a solenoid.

Question. Define a solenoid. How is it different from a coil?
Answer : A coil of many circular turns of insulated wire wrapped closely in the form of a cylinder is called a solenoid.
In a current carrying solenoid magnetic field is same at all points inside it, i.e. field is uniform inside the solenoid. The magnetic field inside a coil vary.

Question. On what factors does the force experienced by a current carrying conductor placed in a uniform magnetic field depend?
Answer : The force experienced by a current carrying conductor in a magnetic field depends upon—
a. length of the conductor
b. current in the conductor
c. magnetic field in which it is kept

Question. Name any three factors on which the magnitude of the magnetic field due to solenoid depends.
Answer : Factors on which the magnitude of the magnetic field due to solenoids
a. number of turns in the solenoid
b. area of cross section of the coil
c. strength of current in solenoid

Question. State the condition for electromagnetic induction to take place. A cylindrical bar magnet is kept along the axis of a circular coil as shown in the figure. Will there be a current induced in the coil if the magnet is rotated about its axis? Discuss.

Answer : Electromagnetic induction
a. Either coil or magnet or both must have a relative motion between them.
b. If there is a change in current in a coil then current will be induced in the another neighbouring coil. No current is induced because there is no change in magnetic field.

Question. Write one difference between direct current and alternating current. Which one of the two is mostly produced at power stations in our country? Name one device which provides alternating current. State one important advantage of using alternating current.
Answer : Direct current has constant magnitude and unidirectional current. Alternating current changes its magnitude and direction alternatively.
a. Alternating current is produced in power stations in India.
b. AG generators are used to produce AC.
c. AC voltage can be increased or decrease with the help of a transformers.

Question. An alpha particle (+ve charged particle) enters a magnetic field at right angle to it as shown in figure.
Explain with the help of a relevant rule, the direction of force acting on the alpha particle.

Answer : Force on a-particle will be in the upward direction as per Fleming’s left hand rule.

Question. What is the nature of magnetic field produced by a straight current carrying circular coil? Explain with the help of an experiment.
Answer : Bend a wire in the shape of a circular loop. Pass the coil through a cardboard. Connect the free ends of the coil to a battery and a key. Sprinkle some iron filings on the cardboard. Put on the key you will find that the iron filings arrange themselves in the form of concentric circles. The magnetic lines of forces near each segment of wire are circular and form concentric circles, whereas the lines of force near the centre of the coil are almost straight lines.
The right hand thumb rule predicts the direction of this magnetic field it states “Grasp the conductor in the right hand with the thumb pointing in the direction of current, and then the direction in which the fingers curl gives the direction of the magnetic field.”

Question. State one main difference between ac and dc. Why ac is preferred over dc for long range transmission of electric power? Name one source each of dc and ac.
Answer : The magnitude and direction of ac remains same whereas a.c. changes its magnitude and direction periodically. Low AC voltage can be increase to high voltage to prevent loss in electric energy during its long distance transmission.
AC generator and DC generator/or cell.

Question. What is meant by the term “magnetic field lines”?
List two properties of magnetic field lines.
Answer : Magnetic field lines are the path traced by a hypothetical north pole in the magnetic field of another magnet or current carrying conductor if it is allowed to do so.
Properties:
a. No two field lines are found to cross each other.
b. Outside the magnet magnetic field lines travel from N-pole to S-pole and inside the magnet from S-pole to N-pole.

Question. Explain what is short-circuiting and overloading in an electric supply.
Answer : When live wire and neutral wire come in contact with each other short circuit takes place. This may be due to fault in electric circuit or when insulation of wire is damaged. During the short circuiting current increases abruptly due to decrease in resistance in the circuit. This short circuiting leads the spark and house may catch fire.
Over loading means to draw the current by all electric appliances in the circuit more than maximum permitted value of the current, overloading also leads the heating of wires which may damage the insulation of wires.

Question. (a) A compass needle gets deflected when brought near a current carrying conductor. Why?
(b) What happened to the reflection of needle when current in the conductor is increased?
Answer : (a) Near a current carrying conductor a magnetic field is produced which deflect the compass.
(b) With the increase in strength of current in the conductor strength of magnetic field also increases so there will be more deflection in compass.

Question. Draw the patterns of magnetic field fines due to a bar magnet. The magnetic field fines are closed curves. Why?
Answer : Magnetic field lines emerge out from the N-pole of a bar magnet go to the S-pole and inside the magnet field lines goes from S-pole to N-pole thus form the closed curves.

Question. State the characteristics of magnetic force.
Answer : If a charge is moving in a magnetic field then it experiences a force known as magnetic force F = qVBsinθ , B is magnetic force, θ is angle between B and V. This magnetic force
a. acts only when charge is moving
b. does not act when charge is at rest
c. is maximum when charge is moving perpendicular to the magnetic field
d. does not act when charge is moving in the same direction of magnetic field.

Question. What are permanent magnet and electromagnet?
Give two uses of each.
Answer : Permanent Magnet: It has constant magnetic field around it. e.g. generator, loud speaker. Electromagnet: When a soft iron is placed in a solenoid it gets magnetised till there is current in solenoid, e.g. electric bells, cranes.

Question. With the help of a neat diagram, describe how you can generate induced current in a circuit.
Answer : Take a coil of large number of turns and connect the two ends of the coil with a galvanometer. Galvanometer is a device used to detect the presence of current. 
Now bring N pole of a strong magnet towards the coil. There is a momentary deflection in the galvanometer. Now bring the N pole away from the coil, again there is a deflection in the opposite direction in the galvanometer deflection in the galvanometer shows that a current is induced in the coil. The induced current can be produced by keeping magnet stationary and giving movement to the coil, or when both have a relative motion w.r.t. each other.

Question. Why is series arrangement not used for domestic circuits?
Answer : In domestic circuits, all appliances are connected in parallel not in series because
a. In series combination same current is passed through each appliances whereas they may need different current.
b. If one appliance fails to work then circuit will be broken and all other appliances will stop to work.
c. If one appliance is switched off others also will stop working i.e. all appliance will work together whether we require it or not.
d. In series combination total potential difference is divided among all appliances in proportion to their resistance. So all appliance will not get required voltage to operate efficiently.

Question. Explain briefly different methods of producing induced emf.
Answer : a. By mutual induction: If we change current in one coil, a current is induced in the neighbouring coil.
b. By giving a relative motion to a magnet and coil in its neighbourhood.

Question. What is the role of fuse, used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating?
Answer : Fuse wire is safety device to prevent electrical devices due to short circuiting or overloading. The fuse wire is rated for a maximum current which has high resistance and low melting point. When there is short circuiting large current is passed in the circuit. Due to large current in fuse wire heat is produced and by melting fuse wire breaks the circuit to keep other appliances safe.
If a fuse wire is replaced by an ordinary copper wire which has low resistance and high melting point it will not melt and domestic appliance may get damaged due to excessive heat due to short circuiting or overloading.

Question. Magnetic field lines are shown in the given diagram. A student makes a statement that magnetic field at X is stronger than at Y. Justify this statement. Also, redraw the diagram and mark the direction of magnetic field lines.

Question. What is meant by the term magnetic field lines? List any two properties of magnetic field lines.
Answer : The imaginary path traced by N-pole of a magnet in a magnetic field is called magnetic field lines. Properties:
a. Two magnetic field lines never intersect each other.
b. Magnetic field lines are crowded near the poles and near the mid part of magnets the density of magnetic lines of force decreases.

Question. Draw a diagram to show how a magnetic needle deflects when it is placed above or below a straight conductor carrying current depending on the direction of the current in the conductor.
Answer :

Question. What is meant by overloading of an electrical circuit?
Explain two possible causes due to which overloading may occur in household circuit. Explain one precaution that should be taken to avoid the overloading of domestic electric circuit.
Answer : Connecting large number of electric appliances in one socket whose load is more than the maximum permitted limit. The two possible cause are
a. all of a sudden supply of high voltage and
b. too many devices connected in a single socket.
Precautions:
a. use of voltage regulator,
b. load of a socket must be greater than its permitted rating.

Question. Name and state the rule to determine the direction of a force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it. Name a device that uses current carrying conductor and magnetic field.
Answer : Fleming’s left hand rule gives the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it. According to Fleming’s left hand rule if we stretch our left hand thumb, forefinger and middle finger in such a way that forefinger points the direction of magnetic field, middle finger points the direction of current then thumb will give the direction of force on the conductor.

Question. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature, (ii) Brushes, (iii) Split ring
Answer : (a) Fleming’s left hand rule: If we stretch thumb, forefinger and middle finger of left hand perpendicular to each other in such a way that forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb will point in the direction of motion/force on the current carrying conductor.
(b) Principle of working of electric motor: A current carrying coil placed in a magnetic field experience a torque. If the coil is free to move it will rotate in the magnetic field.
(c) (i) Armature: The soft iron core on which the coil is wound along with coils is called armature which enhances the power of motor.
(ii) Brushes: Brushes help in transfer of current between coil and external circuit.
(iii) Split rings reverses the direction of current after every half rotation of the coil so that the direction of torque/force on the coil remains and it continuous to rotate.

Question. How does the strength of the magnetic field at the centre of a circular coil of a wire depend on:
a. radius of the coil
b. number of turns in the coil.
Answer : Magnetic field strength at the centre of a circular coil of a wire carrying current 
a. ∝ 1/r , i.e. magnetic field decreases with increase in radius.
b. ∝ n, i.e. magnetic field increases with increase in number of turns.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field should an a-particle (which are positively charged particles) be projected so that it is deflected south ward? Name and state the rule you have used to find the direction in this case.
Answer : Forefinger - direction of magnetic field (upwards). Thumb - direction of force (southwards) Middle finger gives direction of current or direction of positively charged particle (East) i.e. from west to east a particles must be projected.

Question. A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased? Support your answer with a reason.
Answer : If current is increased magnetic field around this conductor increases, the deflection in the galvanometer also increases.

Question. No two magnetic field lines can intersect each other. Explain.
Answer : If two magnetic field lines intersect each other then at the point of intersection there will be two different tangents pointing two different directions of magnetic field at a point which is not possible.

Question. For the circular coil carrying current shown alongside, draw magnetic field lines. Decide which of its face behaves as North Pole and which face as South Pole.
Give reason to justify your answer.

Question. Why does a current carrying Conductor experiences a force when it is placed in a magnetic field? State Fleming’s left hand rule.
Answer : When a current carrying conductor is placed in a magnetic field it experiences a force due to interaction between the two magnetic fields due to current carrying , conductor and given magnetic field of a magnet. If we hold our thumb, forefinger, and middle finger perpendicular to each other in such a way that forefinger points the direction of magnetic field, middle finger points the direction of charge q (direction of current in conductor), then thumb will point the direction force acting upon the conductor.

Question. What are magnetic field lines? How is the direction of magnetic field at a point determined? Mention few important properties of magnetic field lines.
Answer : Magnetic field lines are the path traced by north pole in a magnetic field. A tangent drawn to the magnetic field lines gives the direction of magnetic field at that point.
a. Magnetic field lines emerge out from the N-pole and go to the south pole and from S-pole to N-pole inside the magnet forming the closed curve.
b. They do not intersect each other.

Question. (a) Name the type of electric current generated by the most of the power stations in our country.
(b) Why is it preferred over the other type?
(c) State the frequency of the power supply generated in India.
Answer : (a) Alternating current
(b) AC can be transmitted at high voltage using step up transformer to prevent loss in transmission.
(c) 50 Hz

Question. (a) In a pattern of magnetic field fines due to a bar magnet, how can the regions of relative strength be identified?
(b) Compare the strength of field near the poles and middle of a bar magnet.
Answer : (a) More the density of the magnetic field lines i.e. more closer the magnetic field lines more the strength of magnetic field.
(b) Near the poles magnetic field lines are closer than the middle of a bar magnet. So magnetic strength is more near poles than middle part of bar magnet.