1. Define magnetic lines of forces? How can we plot magnetic lines of force around a bar magnet?

The path along which the unit north pole moves in a magnetic field is called magnetic lines of force or magnetic field lines.

Experiment to plot magnetic lines of force around a bar magnet: - Take a drawing board and fix a white sheet of paper on it. Place a bar magnet at the centre and draw its outline with the help of a pencil. Place the magnetic needle close to any pole. Wait till the needle comes to rest. Draw the dots. Go on marking till the needle comes to other end or pole. Draw a smooth curve using dots. Repeat the process to plot other curves as shown in figure. 

2. Explain the properties of magnetic lines of force?

The properties of magnetic lines of force are:

i)  Magnetic lines of force are closed continuous curves. They start from he north pole and end to the  south pole.

ii) The tangent at any point on the magnetic lines of force gives the direction of the magnetic field at that point.

iii) No two magnetic lines of force can intersect each other.

iv)   Magnetic lines of force are crowded where the magnetic field is strong and far from each other where the field is weak.

3. How can we prove that electricity and magnetism were related phenomena?

Make a circuit by connecting the two terminals of the electric cell to the key as shown in fig. Place a compass needle close to it. Note the direction in which compass needle is pointing. While watching the compass needle carefully, close the key for few seconds. Release the key and watch again. Repeat the steps again by changing its polarity. From this experiment it is observed that the needle gets deflected when we press the key. If the polarity is reversed, the needle gets deflected in the opposite direction. Thus if a current is passed through a wire, electric field is produced near it. This experiment shows that electricity and magnetism are related phenomena. 

4. Explain Right- Hand Thumb Rule?

Imagine that you are holding a current carrying straight conductor in your right hand such that the thumb points towards the direction of current  and  the curled fingers around the conductor will give the direction of the magnetic field. This is known as the right hand thumb rule. 

5. What is a Solenoid? Draw a diagram to show magnetic lines of force through a Solenoid?

A coil of many turns of insulated copper wire wrapped in the shape of cylinder is called a solenoid. 

6. Why alloys like alnico or nipermag are used in industry?

With the help of a solenoid we can magnetise a piece of rod of a given material. If the rod is hard steel and if the magnetic field is strong enough, a permanent magnet can be produced. Permanent magnets are usually made of carbon steel, chromium steel, cobalt and tungsten steel and some alloys. The two such alloys which are used in industry are alnico and nipermag. Nipermag is an alloy of iron, nickel, aluminium and titanium. Alnico is an alloy of aluminium, nickel and cobalt. Permanent magnets of such alloys are used in microphones, electric clocks and many other devices like ammeters, voltmeters etc.

7. What does the force on a current carrying conductor in a magnetic field depend?

Electric current flowing through a conductor produces a magnetic field. The field so produced exerts a force on a magnet placed in the vicinity (nearer) of the conductor.The direction of the force depends on the direction of the current and the direction of magnetic field. The displacement of the rod is maximum, when the direction of the current is at right angles to the direction of magnetic field.

8. Explain Fleming’s left hand rule?

Stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the field and the central finger shows the direction of the current, then the thumb  points towards the direction of motion of the conductor.

9. Which property is used to accelerate charged particles to very high energies?

Current is a flow of charge. This means that moving charges in a magnetic field would experience a force. This property is used to accelerate charged particles to very high energies. These high energies of the particles are used to study the structure of matter.

10. What is an electric motor? Write down the principle of electric motor?

A device which converts electrical energy into mechanical energy is called an electric motor.

Principle of an electric motor: - Electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force.

11. What are the uses of DC motor?

i) These motors are used in domestic appliances like mixers, refrigerators, washing machines etc.

ii) The motors are used in electric fans, hair dryers, record players, blowers etc.

iii) These motors are used in electric cars, rolling mills, electric cranes, electric trains etc.

12. Explain Fleming’s right hand rule?

Stretch the thumb, fore finger and middle finger of the right hand so that they are perpendicular to each other. If the fore finger indicates the direction of the magnetic field and the thumb shows the direction of  motion of conductor, the middle finger will show the direction of induced current.

13. Distinguish between Direct current and alternate current? What is the important advantage of AC over DC?

Direct Current:--

1.The magnitude and direction of the current is constant.

2.This type of current cannot be used on large scale of electricity for house hold purpose.

3.The frequency of direct current is zero.

Alternate Current:--

1.The magnitude and direction of the current reverses periodically.

2.This type of current is used in electrical house hold appliances such as refrigerator, electric heater, iron etc.

3.The frequency of AC current in India is about 50Hz.

An important advantage of AC over DC is that electric power can be transmitted over long distances without much loss of energy.

14. What is an electric generator? Write down the principle of electric generator?

An electric device which converts mechanical energy into electrical energy is called an electric generator.

Principle of electric generator: - Electric generator works on the principle of electromagnetic induction. When the coil of electric generator rotates in a magnetic field, the magnetic field induces a current in this coil. This induced current then flows into the circuit connected to the coil.

15. What are the types of electric generators? Define them?

The two types of electric generators are 1. AC generator, 2. DC generator

1.AC generator: - A generator which converts mechanical energy into electrical energy in the form of alternating current is called AC generator.

2.DC generator: - A generator which coverts mechanical energy into electrical energy in the form of direct current is called DC generator.

16. Describe domestic electric circuit?

The electric power supply for houses and factories are provided by the state electricity board. This is supplied through underground cables or overhead wires or poles. These cables are of three types namely phase wire, neutral wire and earth wire. These wires are connected to an electric meter installed in a house or a factory. The potential difference between phase wire (live wire) and neutral wire is 220v - 250v.The output power from electric meter is taken to the main switch. A fuse known as main fuse is placed in the path of phase or live wire. The output electric power from the main switch is distributed to the domestic electric circuit. In each separate circuit difference appliances can be connected across the live and neutral wires. Each appliance has equal potential difference and they are connected in parallel to each other.

17. Draw a labeled diagram of domestic electric circuit? 

Domestic electric circuit

18. Mention any five safety measures in using electricity?

(1) An electric fuse is a safety device used to save the electrical appliances.

(2) While working with electricity we must wear gloves made of insulated material and rubber soled shoes so that current may not flow through our body.

(3) The insulation of the wire must be checked periodically.

(4) Proper earthing is necessary in order to avoid severe shock.

(5) Electric circuit should be switched off during lightning .This will save the electrical appliances from burning.

19. What is earthing? Why it is necessary?

The systems of connecting the metal casing of an electrical appliance have a metallic body such as electric heater, oven ,refrigerator etc to earth is called earthing. If insulation and wire melt the live wire may  touch the metallic body of the appliance and if we touch this body with bare hands we may receive a severe shock .To avoid this earthing is necessary.

20. What is short circuiting? Mention consequences of short circuiting?

 If a live wire and a neutral wire come in direct contact or touch each other short circuiting takes place During a short circuit, the resistance of the circuit becomes very small and hence huge amount of current flows through it. This produces a large amount of heat and raises the temperature and as a result the circuit catches fire.

21. What is over loading? How can we prevent it?

The flow of large amount of current in the circuit beyond the permissible value of current is called overloading. If many electrical appliances of high power rating such as heater, motor etc are switched on simultaneously, overloading occurs. It may cause fire.

22. Wires carrying electricity should not be touched bare footed. Why?

If we touch the wire barefooted, a large current may pass through our body. So we may receive severe shock. Therefore while working with electricity we must wear gloves made of insulated material and rubber soled shoes so that current may not flow through our body.