CBSE Class 10 Science Magnetic Effects of Electric Current Assignment Set H

Very Short Answer Type Questions :

Question. According to Flemings right hand rule, which part of right hand indicate the movement of conductor?
Answer: Thumb

Question. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer: As per right-hand rule, we find that inside the loop, the magnetic field lines are directed perpendicular to the plane of the paper in the inward direction. Outside the loop magnetic field lines are directed out of the plane paper.

Question. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field is represented by parallel equispaced lines of equal length as follows:

Question. What is the role of the split ring in an electric motor?
Answer: In electric motor, the split ring acts as commutator. Due to its action, the direction of current flowing in motor coil reverses after half turn, giving rise to a continuous rotation of the coil and the axle.

Question. Why is the earth pin thicker and longer than the live and the neutral pins?
Answer: it is thicker so that it does not enter into the live or neutral sockets. It is made longer so that it gets connected to the earth terminal earlier than the live and neutral pins. This ensures the safety of the user.

Question. What is short-circuiting in an electric supply?
Answer: When a neutral wire and live wire come in contact with each other short circuit takes place.

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. (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: Ans : 
(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.

Question. State the direction of magnetic field in the following case:

Answer: Perpendicular to both current and force on the conductor outward the plane of paper.

Short Answer Type Questions :

Question. (a) Draw magnetic field lines of a current carrying circular loop. Identify the region where field is strongest and why?
(b) List two properties of magnetic field lines. 
Answer: (a) On observing the field lines, it shows that magnetic field due to the current carrying circular loop is maximum and normal to the current carrying loop at its center because magnetic field due to each part of loop adds up.
(b) (i) No two magnetic field lines intersect with each other at any point.
(ii) More crowded field lines means a stronger magnetic field.

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. Suppose your science teacher asks you to demonstrate the phenomena of EMI with following materials:
(a)Two different coils land 2 of copper wire having large no. of turns 50 and 100 respectively.
(b) A non conducting cylinder.
(c) A battery
(d) A plug key
(e) A galvanometer
(i) Draw a labeled diagram of your demonstration setup.
(ii) How will you prove the phenomena of EMI.
Answer: (i)

(ii) When key is closed, there is deflection in galvanometer.

Question. Define magnetic field. Describe an activity to draw magnetic field lines around a bar magnet from one pole to another pole.
Answer: Magnetic field is the space around a magnet or a current carrying conductor in which its magnetic force can be experience.
Fix a plane white drawing sheet on a drawing board. Now take a bar magnet and a compass. Place the magnet at the middle of the paper and mark its boundary with the help of a pencil. Now place the compass near its N pole of the magnet and marks the positions of needle of the compass. Now move the compass on the drawing board. Coinciding south pole of the compass with the previous marked point of N pole of the needle and so on, move forward from one end (N pole) to the another end (S pole) of the bar magnet.
Join all the marked points. You will get magnetic lines of force.

Question. Horizontal component of earth’s magnetic field at a place is uniform and its direction is south to north. A high current through a horizontal power line flows at this place from west to east. Consider two points A and B at equal distances from the wire, respectively above and below it. Giving reason explain where is the field more at A or at B.
Answer: The direction of magnetic field due to current at A is from north to south and at B from south to north.
Therefore, at A earth’s magnetic field and field due to current are in opposite direction and at B earth’s magnetic field and magnetic field due to current are in same direction.

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.

Long Answer Type Questions :

Question. Describe in short an activity to:
a. demonstrate the pattern of magnetic field lines around a straight current carrying conductor, and
b. find the direction of magnetic field produced for a given direction of current in the conductor.
Name and state the rule to find the direction of magnetic field associated with a current carrying conductor. Apply this rule to determine the direction of the magnetic field inside and outside a current carrying circular loop lying horizontally on a table. Assume that the current through the loop is anticlockwise.
Answer: (a) Fix a cardboard and pass through its centre a thick copper wire AB connected with a cell of 12 V through a rheostat, an ammeter and plug key as shown in figure. Sprinkle the iron filings uniformly on the cardboard. Plug in the key, tap the cardboard gently a number of times. Iron filings align themselves in a pattern of concentric circles around the copper wire, which represents the magnetic field lines.

(b) The direction of magnetic field so produced around a current carrying conductor can be find with the help of a magnetic compass. When we put a magnetic compass at any point of these field fines it get deflected. The direction of deflection of the compass needle is the direction of magnetic field.

If the direction of current is reversed the direction of magnetic field is also reversed. The direction of magnetic field can be found by using Ampere’s right hand thumb rule. According to it, if we hold a straight conductor in our right hand such that thumb points the direction of current in the conductor .

Question. (a) Describe an experiment with a diagram to show that force is exerted on a current carrying conductor when placed perpendicular in a magnetic field.
(b) How will this force change if current in the conductor is increased?
(c) Name a device that uses the above principle.
Answer: a. Take a small metal rod AB and suspend it from a stand with the help of two connected wire. Put the rod in between the horse shoe magnet in such a way that rod remains in between the two poles. Pass the current in the rod through the two wires.
You would find that the rod is deflected towards the left. Now reverse the direction of current the rod is deflected in opposite direction. This shows that a force is experienced by a current carrying conductor in magnetic field.
b. If the current in the conductor is increased then more force will act on the rod, and get more deflected.
c. Electric motor.

Question. (a) What is meant by a ‘magnetic field’?
(b) How is the direction of magnetic field at a point determined?
(c) Describe an activity to demonstrate the direction of the magnetic field generated around a current carrying conductor.
(d) What is the direction of magnetic field at the centre of a current carrying circular loop?
Answer: a. Magnetic field is the space around a magnet or a current carrying conductor in which its magnetic force can be experienced.
b. A magnetic compass is used to demonstrate the direction of the magnetic field generated around a current carrying conductor.
c. Fix a cardboard and insert a wire to pass through its centre normal to the plane of the card board.
Sprinkle iron filings on card board uniformly. Pass the current in the wire. Tap the cardboard gently.
You will find that iron filings align themselves in the concentric circles around the wire. These circles represents magnetic field lines around the conductor.
d.

At the centre of circular loop, the magnetic field lines are straight.

Question. (a) Which effect of the electric current is utilised in the working of an electrical fuse?
(b) A fuse is connected in series or in parallel in household circuit?
(c) Draw a schematic labelled diagram of a domestic circuit which has a provision of a main fuse, meter, one light bulb and a switch socket.
Answer: a. Heating effect of current
b. In series in the household circuit
c.

Question. (a) When do we state that an electrical appliance is earthed? Mention the function of earth wire in electric lines. Why is it necessary to earth the electric appliances having metallic body?
(b) Explain what is short circuiting and overloading in an electric supply.
Answer: (a) When metal body of an electric appliance is connected to a wire which is connected to a metal plate buried deep inside the earth is said to be electrically earthed.
(b) If due to damaged insulation, live wire and neutral wire come in contact with each other then it is said to be short circuiting overloading. A circuit over load occurs when the amount of current flowing through the circuit exceeds the rating of the protective device. Every electric circuit in a wiring system must be protected against overloading. It happens when too many electric appliances are connected into a single socket.

Question. (a) An electric current is passed in a horizontal copper wire from east to west. Explain your observations when a compass needle is placed (i) below this wire, (ii) above the wire. Draw inference from your observations.
(b) List the factors on which the strength of the magnetic field due to a straight conductor carrying current depend. How should these be changed to decrease magnetic field at a point?
Answer: (a) The direction of deflection of a magnetic compass needle depends upon the direction of the magnetic field at that point. The direction of the magnetic field due to a current carrying wire is given by the right hand screw rule. The direction of magnetic field below and above the wire is opposite so deflection in compass needle changes as well i.e, the deflection is reverse direction.
(b) The factors affecting strength of the magnetic field due to a straight wire carrying current:
1. magnitude of current in the wire α I
2- distance of the point from the wire α 1/I
By decreasing current or increasing the distance of the point from the wire, strength of magnetic field also decreases.

Question. (a) Define electromagnetic induction.
(b) Two coils P and S are wound over the same iron core. Coil P is connected to battery and key the coil S is connected to galvanometer. Draw a suitable diagram of this arrangement and write your observations when:
(i) current in the coil P is started by closing the key.
(ii) current continues to flow in coil P.
(iii) current in coil P is stopped by removing the key.
Explain the reason for such observations.
Answer: a. The phenomenon by producing a current in a coil by changing magnetic field associated with it or by changing a current in the neighbouring coil is called electromagnetic induction. Current so produced is called induced current.
b. (i) When key K is closed due to increasing current a magnetic field is produced which is changing.
In this changing magnetic field coils is kept so an induced current flow through it, so galvanometer shows a deflection.
(ii) After some time current reaches maximum and becomes constant in P coil. There is no change in current so there is no change in magnetic field associated with coil S and hence no induced current in coil S. Deflection in galvanometer becomes zero.

(iii) Current becomes zero from maximum in coil P and hence galvanometer shows a deflection but now it is in opposite direction.

Question. Two coils C1 and C2 are wrapped around a nonconducting cylinder. Coil C1 is connected to a battery and key and C2 with galvanometer G. On pressing the key (K), current starts flowing in the coil C1 State your observation in the galvanometer.

a. What key K is pressed on.
b. When current in the coil C1 is switched off.
c. When the current is passed continuously through coil C1.
d. Name and state the phenomenon responsible for the above observation. Write the name of the rule that is used to determine the direction of current produced in the phenomena.
Answer: a. Induced current in coil C2 is produced so galvanometer shows a deflection.
b. Again galvanometer shows a deflection but in opposite direction to the previous one.
c. There will be no deflection in galvanometer.
d. This phenomenon is called electromagnetic induction. The phenomenon in which a changing magnetic field in a coil induces a current in another coil kept near it. Fleming’s right hand rule is used to find the direction of induced current.

Question. (a) The given figure shows a domestic electric circuit.
Study this circuit carefully. List any two errors in the circuit and justify your answer.

(b) Give one difference between the wires used in the element of an electric heater and in a fuse.
(c) List two advantages of parallel connection over series connection.
Answer: (a) Errors in the circuit
(i) Fuse wire is connected in neutral wire (N) where as it must be connected in live wire (L).
(ii) Circuit of bulb B2 is incomplete.
(b) Element of electric heater has high resistance and high melting point whereas a fuse wire has high resistance and low melting point.
(c) Advantages of parallel connection over series connection.
(i) In parallel combination if one appliance fails to work others keep working.
(ii) Potential difference across each appliance remains same.

Question. What is a solenoid? Draw the magnetic line of forces for solenoid and a bar magnet. Compare the two and state one similarity.
Answer: A solenoid is a large number of turns of insulated copper wires having shape of a cylinder or helix.
Magnetic field are given in following figures.

(a) Fix a white paper sheet on a drawing board with the help of copper pins. Keep a bar magnet in the centre of the paper and sprinkle some iron filings uniformly around the bar magnet. Tap the board gently. Iron filings arrange themselves in a pattern as shown in figure. These iron filings near the bar magnet align themselves along the magnetic field lines.
(b) A current carrying solenoid behaves as a bar magnet one end of the solenoid behaves like a N pole and another end as S pole like two poles in bar magnet, so the field lines of a solenoid and bar magnet appear same in many ways:
(i) Magnetic lines of force inside the body is strong and uniform.
(ii) In both the cases stronger field exists at the poles compared to the middle part.
Dissimilarities
(i) In bar magnet, the poles are not exactly at the ends of the magnet, in solenoid poles can be considered to be lying at the edges.
(ii) In bar magnet, magnetism is permanent but in solenoid it exists only till there is a current in solenoid.

Question. Answer the following questions:
a. What is the direction of magnetic field lines outside a bar-magnet?
b. Why two magnetic field lines cannot intersect each other?
c. What is indicated by crowding of magnetic field lines in a given region?
d. What is the frequency of ac in India?
e. State one advantage of ac over dc.
Answer: a. From N pole to S pole
b. If two magnetic field lines would intersect each other then at the point of intersection there would be two different directions of magnetic field which is not possible.
c. Magnetic field strength is more in that region.
d. 50 cycles per sec (c/s) or Hz.
e. AC can be step up for transmission over a longer distances with less power loss.

Question. What is meant by magnetic force? Name and explain the rule to determine the direction of force experienced by a current carrying conductor in a magnetic field. How does this force gets affected on:
(i) doubling the magnitude of current, (ii) reversing the direction of flow of current, (iii) reversing the direction of magnetic field.
Answer: The force experienced by a current carrying conductor when placed in a magnetic field or the force experienced by a charged particles moving in a magnetic field is called magnetic force.Fleming left hand rule: According to this rule, on stretching the thumb, forefinger and the middle finger of your left hand such that these are perpendicular to each other, if the force finger points in the direction of magnetic field and middle finger in the direction of current, then the thumb will point in the direction of motion of force acting on the conductor.
(i) If magnitude of current is doubled, then force is doubled.
(ii) If direction of flow of current is reversed, the direction of force is also reversed.
(iii) If direction of magnetic field is reversed, the direction of force is also reversed.