# MAGNETIC EFFECTS OF ELECTRIC CURRENT

By | June 28, 2017

Magnetic effects of electric current

Ques.1 State the properties of magnet?

Ans.1

• Magnets are of many shapes-bar magnet, hours shoes magnet, round magnet etc.
• A magnet has 2 poles- South pole and north pole unlike poles attract and like poles repel.
• Magnetic field line emerge from north and enter the south pole.

Ques.2 Draw a well-labelled diagram of magnetic field lines of a bar magnet?

Ans.2   Diagram Ques.3 State properties of magnetic field lines?

Ans.3

• They emerge from north pole and enter the south pole and forms concentric circles outside the magnet.
• Inside the magnet, they move as parallel line from south pole to north pole.
• Magnetic fields line have both direction & magnitude.
• No two field lines intersect  line each other.

Ques.4 Why does the compose needle gets deflected when brought near bar magnet?

Ans.  This is because compass needle is also a small magnet, When it is brought near a bar magnet, it gets attracted or repelled by the poles of magnet.

Ques.5 What is a magnet field?

Ans.5 The region surrounding a magnet in which the force of the magnet can be detected is called a magnetic field. The magnetic field is a quantity that has both magnitude and direction.

Ques.6 Draw a diagrammatic sketch to show the pattern of field lines around a straight conducting wire.

Ans.  Diagram Ques.7  How will you find the direction of the magnetic field around a straight current carrying conductors?

Ans.7  For finding the direction of the magnetic field around a straight conduct carrying conductor we will use right-hand thumb’s rule which state when we point the thumb in the direction of current, the direction of fingers gives us the direction of the magnetic field lines.

Ques. 8 Why don’t two magnetic field lines intersects?

Ans.8 This is because, if they did, if would mean that at the point of intersection the compass needle would point towards two direction which is not possible.

Diagram… Ques.9  With the help of diagram explain the magnetic field produced y a current carrying circular loop?

Ans.9  Diagram In a loop conducting wire every point on the wire carrying current would give rise to the magnetic field appearing as concentric circles around it,  by the time we reach centre of loop, the arcs of these circles would  appear as straight lines by applying the right hand thumbs rule we would indicate direction of magnetic fields lines around the loop. Every section  of wire contributes to the magnetic fields line in the same direction within the loop.

Ques.10 On what factors does the magnetic fields produced  by current carrying conductors depend?

Ans. The magnetic field produced by current carrying conductor depends on following:-

1. Directly on current passing through it .
2. On the number of turns wire, if the turns increase n times , then the fields becomes n times and vice-versa.

Ques.11 What is a solenoid? Draw its labelled diagram.

Ans.11 Diagram A coil of many turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid . One end of the solenoid behave as magnetic north pole while other one behaves a south pole on passing current through it. The pattern of magnetic field lines is exactly of the form of bar magnet. Inside the solenoid the magnetic field is uniform at all places.

Ques.12  State applications of solenoid.

Ans.  A strong magnetic field produced inside a solenoid can be used to magnetise a piece of soft iron when placed inside the coil, the magnet so formed is called  an electromagnet.

Ques.13. The  magnetic field in a given region is uniform. Draw a diagram to represent  it.

Ans.13 Ques.14 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 inside and outside loop.

Ans.14 In the centre of the loop , the field is from west to east. At the top of the loop, the field is from north to south. At the bottom of loop, field is from south to north.

Ques.15 Suggest 2 methods to produce magnetic field.

Ans.15

• By having a magnet which has magnetic field around it.
• By passing current through conducting wire which will produce magnetic field.
• We can change wire to solenoid and passing current through it, this will be similar to a bar magnet.

Ques.16 Can you identify the south and north pole of current carrying solenoid with help of bar magnet? Explain.

Ans. 16 When current is passed through solenoid, it behaves like a magnet, we can determine the south and north pole by bringing bar magnet near it.

Ques.17 A current through a horizontal power line flows in east to west direction, what is the direction of magnet field directly above it and below it?

Ans. 17 Diagram The direction of magnetic field just above and below the point would be from north- south or south to north.

Ques.18 State Fleming’s left hand rule.

Ans.18 It States: When the index, middle finger and thumb of the left hand are perpendicular to each other or right angled at each other, the index finger point in direction of magnetic field, the middle one gives direction of current and the thumb will point in the direction of the motion or force acting on conductor. Ques. 19 On what factors does the force acting on the  conductor depends?

Ans.19 The direction of force  acting on conductor depends upon the direction of the current and the direction of magnetic field.

Ques.20 When is the displacement of the rod or the magnetic of the force highest?

Ans.20 The magnitude of the force or displacement is highest when direction of current is at right angle to the  direction of magnetic field .

Ques.21 With the help of activity, prove fleming’s left hand rule?

Ans.21

• Take a small aluminium rod AB using two connecting wires suspend it horizontally from a stand.
• Place a strong horse-shoe magnet in such a way that the rod line between the 2 poles with the magnetic field directed upwards.
• Connect the aluminium rod in series with a battery, key, rheostat.
• Now pass a current through the rod from A to B.
• It is observed that rod is displaced to left.
• Reverse the direction of current and observe direction of displacement. it is now towards right.

Diagram Ques.22 What is an electric motor? State its principle.

Ans.22 It is a rotating device that converts electrical energy into mechanical energy,it works on the principal of Fleming’s left hand rule. It is used as an important component in electric fans, mixers, refrigerators, washing machine, computers, mp3 players.

Ques.23 What is electromagnetic induction? Who studied it for the first time?

Ans.23 It was studied by Michael Faraday discovering how a moving magnet can be used to generate electric current. Electromagnetic induction is the production of induced current in a coil placed in a  region where magnetic field changes with time. The direction of current is given by Fleming’s right hand rule.

Ques.24 What is galvanometer?

Ans.24 It is a device that can detect the presence of very small amount of current in a circuit.

Ques.25 State Fleming’s right hand rule?

Ans.25 If we place the index, middle, and thumb finger mutually perpendicular to each other. The 4 finger indicates the direction of magnetic field, the middle finger indicates of induced current  and thumb indicates movement of conductor.

Diagram Ques.26 When is the induced current is found to be highest?

Ans.26 When the direction of motion of coil is at right angle to the magnetic  fields. The induced current is highest.

Diagram Ques.27 What does this experiment indicates?

Ans.27 It indicates that potential difference is induced in coil 2 whenever the electric curent through coil 1 is changing. Coil 1 is the primary coil and coil 2 is secondary coil as current in coil 1 changes, its magnet field also changes, thus magnetic fields around coil 2 also changes. This induces current in coil 2 . this show the phenomenon of electromagnetic induction.

Ques.28 Explain different ways to induce current in a coil?

Ans.28 We can do it either by moving it in a magnetic fields or by changing the magnetic field around it.

Ques.29  What is an electric generator? State the principle and uses?

Ans.29 It works on the principle of electromagnetic induction , it converts  mechanical energy into electricity energy . It is used to get electricity in AC and DC form.

Ques.30 Name Some sources of direct current?

Ans.30 DC generator,  cells, batteries.

Ques.31 Which source produce alternative current?

Ans.31 AC generator & domestic circuits.

Ques.32 Name 2 safety measures commonly used in electric circuits and appliance.

Ans.32 Electric fuse, Earth fuse.

Ques.33 Which are the 3 wire used in a domestic circuits?

Ans. 33 Red wire(live wire), Black wire(neutral), green wire( earth wire).

Ques.34 What is the purpose of the earth wire?

Ans.34 It is usually connected to a metal plate deep under the earth near the house. It is for those appliances which have metal body. For example: refrigerator, microwaves,  etc.  It provide a low resistance conducting path for the current. Thus it ensures that any leakage of current to the metal body of the appliances it keeps it potential to that the earth and the user may not get a severe shock.

Ques.35 What precautions should be taken to avoid the overloading of domestic circuits?

Ans.35 To avoid overloading of the domestic circuits, fuse should be introduced in the circuit. We should  not attach many appliances on a single plug socket. The insulation of wires should be checked periodically  to avoid short circuits.