Worksheet - Magnetic Effects of Electric Current

 Magnetic Effects of Electric Current - Solved  Worksheet

Recall

Magnetic Field Due to a Current Carrying Conductor

When electric current flows through a current carrying conductor, it produces a magnetic field around it. This can be seen with the help of a magnetic needle which shows deflection.

The more the current, the higher the deflection. If the direction of current is reversed, the direction of deflection is also reversed  Magnetic Effect of Electric Current

Right Hand Thumb Rule

It is used to find the direction of the Magnetic Field around a current carrying conductor.

Properties of Magnetic Field: 

• The magnitude; of magnetic field increases with increase in electric current and decreases with decrease in electric current. 
  
  
• The magnitude of magnetic field; produced by electric current; decreases with increase in distance and vice-versa. The size of concentric circles of magnetic field lines increases with distance from the conductor, which shows that magnetic field decreases with distance. 
  
  
• Magnetic field lines are always parallel to each other. 
  
  
• No two field lines cross each other.

Solenoids

A Coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called solenoid

The strength of the magnetic field produced depends upon 

(a) The number of turns 

(b) Strength of current in the solenoid used in making solenoid

(c) The magnetic field of the Solenoid resembles as that of the magnetic field of the bar magnet and the
      Earth.

Force on a Current carrying Conductor in a Magnetic Field

A current carrying conductor when placed in a Magnetic field experiences a force due to which it moves or rotates.

The direction of force on the current carrying conductor is determined with the help of Fleming Left Hand Rule.

Fuse 

In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. 

A fuse is a small, thin conductor designed to melt and separate into two pieces for the purpose of breaking a circuit in the event of excessive current due to overloading or short circuiting,

Short-circuit 

A short circuit is simply a low resistance connection between the two conductors supplying electrical power to any circuit. This results in excessive current flow in the power source through the 'short,' and may even cause the power source to be destroyed. It can occur also when live wire and Neutral wire comes in touch with each other. In this situation, heavy current is drawn from the mains, if not avoided; it will burn the conducting wires and the connected devices. 

The FUSE acts as a protecting mechanism. A fuse is a small piece of conductor with a low melting point. It melt in case current exceeds in case of short-circuit or overload.

Overloading 

Overloading of electrical circuit occurs, when the number of appliances operated on the circuit at the same time exceeds the limits the circuit wiring can withstand. In domestic circuits all the appliances are connected in parallel; and in parallel connection , the total current from the mains will sum of the individual current drawn from each of the devices. 

Here again the FUSE is used a protecting mechanism.

Overloading can also occur during Lightening (during rainy season) inducing High Voltage in the power supply line.

Earthing

Earthing or Grounding is a safety mechanism. It is used to protect human being from getting an electric shock. The electrical devices with the mechanical body like coolers, Ions and geysers etc. When comes in touch with the Live wire due to some internal fault in device. This makes the body of the equipment at the potential of the Live wire. The Earth is a good conductor of electricity. The person standing on ground if touches the metallic body of the device. The electric current will flow through the human body resulting in electric shock resulting immediate death of the person.

For details Notes- Please visit :  Magnetic Effect of Electric Current Notes

Check your Concepts:

1. The most suitable material for making the core of an electromagnet is: 

a) Steel 

b) Iron 

c) Soft iron 

 d) Aluminum

Answer: c

2. When a straight conductor is carrying current: 

a) There are circular magnetic field lines around it 

b) There are magnetic field lines parallel to the conductor 

c) There are no magnetic field lines 

d) None of the above

Answer: a

3.Two magnetic field lines: 

a) Intersect at the neutral point 

b) Never intersect each other 

c) Intersect near north-pole or South Pole 

d) Intersect at the midpoint of the magnet

Answer: c

4. A student learns that magnetic field strength around a bar magnet is different at every point.

    

    Which diagram shows the correct magnetic field lines around a bar magnet?

Answer: c

5. The magnetic field inside a long straight solenoid carrying current: 

a) Is zero? 

b) Decrease as we move towards its end 

c) Is the same at all points? 

d) Increase as we move towards its end

Answer: c

6. A student places some iron filings around a magnet. The iron fillings arrange themselves as shown in the image. 

The student labeled four different regions around the magnet. Where would the magnetic field be the strongest? 

(a) P 

(b) Q 

(c) R 

(d) S

Answer: c

7. A metal rod PQ is placed in the magnetic field. The ends of the rod are connected to a battery using wires. 

Where will the rod move? 

(a) Upward 

(b) Downwards 

(c) Into the field 

(d) Out of the field

Answer: d

8. A soft iron bar is introduced inside a current-carrying solenoid. The magnetic field inside a solenoid: 

a) Decrease 

b) Will increase 

c) Will become zero 

d) Will remain unaffected

Answer: b

9. Appliances that have a metal body are generally connected to the earthing wire. What is the reason to earth these wires? 

(a) To prevent the excess current 

(b) To prevent the leakage of current 

(c) To provide extra current to the appliance 

(d) To provide high resistance to the appliance

Answer: b

10. Which of the following correctly describes the magnetic field near a long straight wire? 

a) The field consists of straight lines perpendicular to the wire 

b) The field consists of straight lines parallel to the wire 

c) The field consists of radial lines originating from the wire 

d) The field consists of concentric circles centered on the wire

Answer: d

11. Magnetic effect of current was discovered by 

(a) Oersted 

(b) Faraday 

(c) Bohr 

(d) Ampere

Answer: a

12. The instrument that use to detect electric current in the circuit is known as 

(a) Electric motor 

(b) A.C generator 

(c) Galvanometer 

(d) None of the above

Answer: c

13. If the key in the given arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are – 

(a) Concentric circles 

(b) Elliptical in shape 

(c) Straight lines parallel to each other 

(d) Concentric circles near the point O but of elliptical shapes as we go away from it

Answer: a

14. 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

15. Switches are connected to – 

(a) live wire. 

(b) Neutral wire. 

(c) Earth wire. 

(d) Any one.

Answer: a

16. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane and on the axis of the coil) is anticlockwise and clockwise respectively. The magnetic field lines point from B to A. The N-Pole of the resultant magnet is on the faces close to – 

(a) A 

(b) B 

(c) A if the current is small, and B if the current is large 

(d) B if the current is small, and A if the current is large

Answer: a 

Actually, the magnetic fields emerge from North Pole of magnet, and go into the South Pole. 

17. In the arrangement shown in the figure there are two coils on a non-conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then

 

(a) The deflection in the galvanometer remains zero throughout 

(b) There is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed 

(c) There are momentary galvanometer deflections that die out shortly, the deflections are in the same direction. 

(d) There are momentary galvanometer deflections that die out shortly, the deflections are in the opposite direction.

Answer: a

There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions. When the key is inserted in the circuit of coil 1, there is a momentary increase of current. This change in current produces a change in the magnetic field. Since changing magnetic field induces a current, a momentary deflection is seen in the circuit of coil 2. 

Similarly, on removing the key, the current becomes zero quickly, and there is a change in the current in coil 1. And, this current change induces a current in coil 2. But this time the deflection happens in the opposite direction.

18. The strength of magnetic field inside a long current carrying straight solenoids is – 

(a) more at the ends than at the center 

(b) minimum in the middle 

(c) same at all points 

(d) found to increase from one end to the other

Answer: c 

The magnetic field lines inside a current carrying solenoid are parallel and equidistant which means the strength of magnetic field is uniform inside the solenoid i.e. same at all points.

19. Magnetic field lines 

(a) have one direction at a point 

(b) have no physical reality 

(c) can be used to indicate the direction of the magnetic field of a point 

(d) all the above

Answer: d

20. A current carrying wire in the neighborhood produces 

(a) no field 

(b) electric and magnetic fields 

(c) Electric field only 

(d) magnetic field only

Answer: b