1. Electric Circuit: A conducting path consisting of source, load, switch connected by conducting wires through which current can flow is called electric circuit.
2. Open Circuit: The circuit in which switch is off or current doesn’t flow is called open circuit.
3. Closed circuit: The circuit in which switch is on or current flows is called closed circuit.
4. Electric Load: The appliance which converts electric energy into other forms of energy is called load. It is also called resistors.
5. Series combination of cells: The combination of cells where positive terminal of one cell is connected with negative terminal of another cell and so on is called series combination.
6. Characteristics of series combination of cells
i. Total voltage gets added, i.e. V=V1+V2+V3
ii. Magnitude of current increases by increasing number of cells.
7. Parallel combination of cells:
It is a type of combination where all positive terminals of cells are connected at one common point and negative at another.
8. Characteristics of Parallel Combination of Cells:
i. Total voltage obtained is always same. i.e.V=V1=V2=….
ii. Magnitude of current cannot be increased in this combination.
iii. It provides current for longer time.
9. Characteristics of series combination of resistors.
i. Resistors and connected end to end.
ii. Current is same in all resistors but voltage gets divided.
- Equivalence resistor is given as; R=R1+R2+R3
10. Characteristics of parallel combination of resistors:
i. Resistors are connected in between two common points.
ii. Potential difference is same in all resistors but current gets divided.
- It any resistor fails to work, rest of resistor works.
- Equivalence resistance is given as: = ++
11.
| D.C | A.C |
| 1. There is no change in polarity with time. | 1. There is change is polarity with time. |
| 2. It is produced by battery and D.C. generator. | 2. It is produced by dynamo and A.C. generator. |
| 3. It’s voltage cannot be altered by transformer. | 3. It’s voltage can be altered by transformer. |
12. Features of domestic circuit.
i. All the electrical appliances are connected in parallel.
ii. Different coloured wire are used for live, neutral and earthling wire.
13. Things to be remembered for house hold wiring.
i. Switch and fuse must be connected in live wire.
ii. Appropriate fuse should be use.
iii. Separate fuse should be used for room, floor and house.
iv. Separate lighting and power circuit should be used.
- Wiring should not be done in damp and water leaking areas.
14. Electric power: It is defined as the rate of conversion of electrical energy into other forms of energy by electrical appliance.
Electric power (P) = Voltage (V) x current (I) [P=IV]
15. 1 Kilowatt hour: It is defined as the energy consumed by an electric appliance of power one kilowatt for one hour. [1 kwh=1unit]
16. Relation between kwh and joule.
We have, 1 kwh = 1 unit
= 1000 watt hour
= 1000 x 3600 seconds
= 3600000 Joules
\1 kwh = 3.6×106 Joules
17. Fuse: It is a safety measure which protect circuit from excessive heating. It is a metal wire made of tin and lead having low melting point. It is connected in series.
18. Overloading: If extra electrical appliances are used in the circuit beyond its capacity, it damages the wire by drawing large current, it is known as overloading.
19. Short circuit: If positive and negative wires are connected together in the circuit, it generates large amount of current and electric sparks is seen. This is known as short circuit.
20. Effects of current electricity:
i. Heating effects. ii. Lighting effects
iii. Chemical effect iv. Magnetic effects
21. Heating effect: A conductor gets heated when electric current is passed through it, which is known as heating effect. This effect is applicable to the appliances which converts electrical energy to heat energy such as electric iron, kettle, heater, etc.
22. Heating element: A coil of wire having high resistance which is used in heating devices is known as heating element. Generally, nichrome wire (alloy of Nickel and chromium) is used as heating elements.
23. Nichrome wire is used as heating element for following reasons:
i. It has high melting point.
ii. It has high resistance.
iii. It does not react with oxygen even at temperature of 9000C.
24. Lighting effect: The phenomenon of conductor to emit light when it is very hot is known as lighting effect. Electric lamp converts electrical energy to light energy by lighting effect.
25. Differentiate between Filament Lamp and Fluorescent Lamp
| Filament Lamp | Fluorescent Lamp |
| 1. Tungsten metal used as filament when heated emit light. | 1. Fluorescent power coated on inner wall of tube emits light |
| 2. Its life duration is about 1000 hours. | 2. Its life duration is about 3000 hours. |
| 3. Inert gases like argon and nitrogen or filled up. | 3. Mercury vapour is filled inside tube. |
| 4. Its efficiency is about 10%. | 4. Its efficiency is about 30%. |
26. Magnetic Effect: When an electric current is passed through a conductor, it behaves like a magnet. This is called magnetic effect of electric current.
27. Electromagnet:: A solenoid which behaves like a magnet during the flow of electric current through it is known as electromagnet.
28. Solenoid: The coil of insulated wire used to make electromagnet is known as solenoid. (Spiral adjustment of insulated wire)
29. Strength of electromagnet can be increased by:
i) Increasing the number of turns per unit length of coil.
ii) Increasing the amount of current
iii) Using soft iron core in the coil.
30. Chemical effect: When current is passed through a liquid it undergoes chemical change. This effect is known as chemical effect of current.
31. Electrolyte: Substance which allows electric current to pass through them in aqueous form is known as electrolyte. Eg, HCl, NaCl, etc.
32. Electrolysis: The process of decomposition of electrolytic solution in to its constituent by passing of electricity is known as electrolysis.
33. Electroplating: The process in which a thin layer of one metal is coated over another metal by use of electrolysis process is known as electro plating.
34. Points to be considered during electroplating.
i) The metal which is to be coated should be made cathode.
ii) The metal to be deposited should be made anode.
- The electrolyte used
35. Applicator of electrolysis:
i) It is used for purification of metals.
ii) It is used to manufacture of hydrogen and oxygen gas.
- It is used in electroplating.
- It is used in electrotyping.
36. Electromagnetic induction: The phenomenon in which current is induced by change in magnetic flux by a conducing wire is called electromagnetic induction.
37. Magnetic flux: Magnetic flux through a surface is defined as the number of magnetic lines of force passing through the surface held perpendicular to these lines of force.
38. Faraday’s laws of electromagnetic induction:
i) Whenever magnetic flux linked with a closed circuit changes, an induced e.m.f. is produced in the circuit.
ii) The induced e.m.f. lasts as long as the change in magnetic flux is taking place.
iii) The magnitude of the induced e.m.f is directly proporral to the rate of change of magnetic flux.
39. Fleming’s ring hand rule: The method of finding the direction of induced current by use of three fingers of right hand is called Fleming’s right hand rule. It states if first three fingers of right hand are held mutually perpendicular to each other, the fore finger, the thumb and central finger give the direction of magnetic field, motion and induced current respectively.
40. Generator or dynamo: Machines used to convert mechanical energy in to electrical energy is called generator or dynamo. They are based on principal of electromagnetic induction. Generally dynamo is used to induce current in less amount. While generator is used to induce large scale. Fleming’s right hand rule is used to determine directon of induced current.
41. Magnitude of induced e.m.f. in generator/ Dynamo can be increased by following:
i) Increasing number of turns in coil.
ii) Increasing strength of magnetic field.
iii) Increasing speed of rotator of magnet near the coil.
iv) Decreasing the distance between magnet and coil.
42. Motor effect:
When a current carrying conductor is kept in a magnetic field the conductor moves if it is allowed to do so. This is called motor effect.
43. Electric motor: A machines used to convert electrical energy in to mechanical energy is called electrical motors. It works on principal of motor effect. It is used in appliances suchas, electric fans, washing machine, refrigerators, etc.
44. Transformer: A device used to increase or decrease the magnitude of alternating e.m.f. is called transformer.
It is of two types step up and step down.
| Step up transformer | Step down transformer |
| 1. Low voltage is converted in to high voltage | 1. High voltage is converted in to low voltage. |
| 2. Number of turns primary coil is less. | 2. Number of turns im primary coil is larger. |
| 3. Number of turns in secondary coil is more. | 3. Number of turns in secondary coils is les. |
| 4. It increases the magnitude of A.c. e.m.f. | 4. It decreases the magnitude of A.C. e.m.f. |
45. Uses of transformer:
i. For transmission of A.C current through a long distance, step up transformer is used.
ii. Step down trans former are used in voltage regulator of computer, television, radio, etc.
REASONABLE FACTS
1. Combination of cells is done.
Ans- Combination of cells is done in order to increase or decrease the amount of electric current and potential difference (voltage)
2. Cells are connected in parallel.
Ans- In order to gain more amount of current than that delivered by a single cell, a no. of cells are connected in parallel.
3. Cells are connected in series.
Ans- In order to gain more amount of voltage than that of the electromotive force (e.m.f.) of a single cell, a no. of cells are connected in series.
4. Tungsten wire is used as a filament in a bulb.
Ans- Since, the tungsten wire has high resistivity and high melting point (about) 34000C), it is used as a filament in a bulb.
5. The filaments of the bulbs are made of very thin wire.
Ans- In order to increase the resistance to high value, the filaments of the bulbs are made of very thin wire since the resistance of coil changes with the thickness of the coil (as R¥1/a).
6. Mercury vapour is filled in a fluorescent lamp.
Ans- Mercury vapour is filled in a fluorescent lamp in order to produce UV-rays and also for providing the conduction of electricity inside the tube, when it is lionized.
7. Inner wall of a fluorescent lamp is coated with fluorescent power.
Ans-Inner wall of a fluorescent lamp is coated with fluorescent power because fluorescent power absorbs the UV-rays and emits visible light.
8. Insert gases are filled in a filament lamp.
Ans- Inert gases (Ar, Ne, N etc.) are filled in a filament lamp in order to prevent the filament from vapourisation when heated to a high temperature of about 29000C.
9. Air is not filled in electric bulb.
Ans- Air is not filled in electric bulb as tungsten reacts with oxygen of air at high temperature and the filament is destroyed due to oxidation.
10. Earthing is done.
Ans- Earthing is done in order to protect the user from any accidental electric shock and to save the electric appliances from being damaged in case of short circuit and overloading.
11. Earthing is required in case of electric appliances having metallic bodies.
Ans- Earthing is required in case of electric appliances having metallic bodies in order to avoid electric shock during their use.
12. Earthing is done only on the outer part of the electric appliances.
Ans- Earthing is done only on the outer part of the electric appliances as the leaked charges and excess charges from the outer part move to the ground and get neutralized and prevents from electric shocks.
13. Nichrome is used as a heating elements in electric iron, heater.
Ans- Nichrome has high resistance, high melting point and does not react with oxygen of air even at a high temperature of about 9000C but tungsten does. So, nichrome is used as a heating element in electric iron, heater but not tungsten.
14. A fuse always connected to the live line (or phase wire).
Ans- A fuse always connected to the live line and in series with the electric circuit to break the electric circuit completely during the required period, as the current enters through live wire.
15. A copper wire cannot but used as a fuse wire.
Ans- A copper wire cannot be used as a fuse wire because it has high melting point and low resistance so that it will not melt easily as soon as short circuiting or overloading occurs in an electric circuit.
16. Filament lamp is dimmer than fluorescent lamp of same power.
Ans- Filament lamp is dimmer than fluorescent lamp of same power because the fluorescent lamp converts 30% of the total electrical energy in to light energy but the filament lamp converts only 10% of the electrical energy.
17. A current carrying conductor deflects magnetic needle.
OR
Ans- A current carrying conductor affects magnetic needle placed near it.
Ans- When a current passes through a conductor, according to Oersted, the space around the conductor is magnetized .i.e. there is a magnetic field around the conductor. Due to this magnetic field, the magnetic needle is affected.
18. A current carrying conductor placed in a magnetic field experiences a force.
Ans- A current carrying conductor has magnetic field around it i.e. current carrying conductor is a magnet. There is an interaction between two magnets. Hence, if a current carrying conductor is placed in a magnetic field, the conductor experiences a force.
19. Domestic wiring is not done in series circuit.
Ans- Domestic wring is not done in series circuit due to the following reasons:
– If one line is overloaded or short circuited, the fuse in the whole circuit is blown off and other distribution circuit are also gets affected.
– If the electric power is to be switched off in a room for repairing or any other purposes, the electric power in whole circuit is blown off.
20. All the electrical equipments are connected in parallel in domestic circuit.
Ans- All the electrical equipments are connected in parallel in domestic circuit due to the following reasons:
– Each electrical equipment can be operated with separate witch.
– If one of the electrical equipments fails to work, other equipment keep on working.
– The potential difference across each electrical equipment is same as the potential of main line and many devices can be operated with the same potential difference line.
21. MCB is used in household wiring.
Ans- MCB is used in household wiring in order from over landing or short circuit.
22. Bulbs are connected in parallel in domestic wiring.
Ans- Bulbs are connected in parallel in domestic wiring due to following reasons:
– Each bulb can be operated with separates switch.
– The bulbs keep on working when there is failure in working of other devices.
23. A switch is always connected to the live line.
Ans- A switch is always connected to the live line to disconnect the electric supply to electrical appliances when the switch is off.
24. An electric switch should not be touched with wet hands.
Ans- Since the water is semi-conductor of electricity and an electric current can flows through our body causing electric shock so electric switch should be not be touched with wet hands.
25. Electromagnet is widely used in electrical appliance.
Ans- Electromagnet is widely used in electrical appliances due to the following reasons:
– Electromagnet is temporary and the magnetic property can be developed according to our need.
– The electromagnet of desired shape and size and power can be made.
26. A step-up transformer is used between the electric tower and the power generating station.
Ans- Converting electricity at low voltage- high current to high voltage-low current is done by step-up transformer so it is used between the electric tower and the power generating station.
27. The core of transformer is laminated.
Ans- The core of transformer is laminated because lamination reduces energy loss in the form of heat across the transformer. But, if the core is a single block of iron instead of laminated core, there will be heating effect on the core and we get less output.
28. Soft iron core is used in a transformer.
Ans- Soft iron core increases the magnitude of induced e.m.f. in the secondary coil of a transformer so it is used in a transformer, as the soft iron has higher magnetic permeability.
29. Tungsten cannot be used heating elements in heater iron.
Ans- Tungsten oxidizes at the high temperature when exposed to air. So, it cannot be used as heating element in heater or iron.
30. The use of alternating current would be limited if transformer were not invented.
Ans- Transformer is used to convert low voltage AC into high voltage AC and vice versa. The use of alternating current would be limited, if transformer were not invented because
i) The conversion of low voltage AC into high voltage AC in power stations would be impossible.
ii) It would be impossible to operate the electric appliances which require a low voltage AC.
31. The number of turns in the primary and secondary coil of a transformer are never made equal.
Ans- A transformer is used to convert a low voltage alternating e.m.f into high voltage alternating e.m.f. by increasing the no. of turns in the secondary coil. Similarly a high voltage alternating e.m.f. is changed into a low voltage alternating e.m.f. by decreasing the number of turns in the secondary coil. Since the magnitude of induced e.m.f. is directly proportional to the ratio of number of secondary turns, the number of primary and secondary turns is never made equal.
32. In the electroplating process, the object on which electroplating is to be done, must be made cathode.
Ans- During electroplating the positively charged ions become neutral by gaining electrons and are deposited on cathode. Therefore, the object on which electroplating is to be done must be made cathode.
33. Most of the electrical appliances are marked with 220V.
Ans- Every electrical appliance must be marked with the correct voltage range and the voltage applied must lie. 220V is the main AC electrical supply value. The voltage is the average value for most general purpose current measures. It calculates the total electromotive force and the fatal resistance in the electric wires. Hence, the reason.
34. MCB’s are for better then fuse wire.
Ans- It is because MCB’s switched off the circuit within the fraction of a second in case of overloading or short circuit. The MCB can be reset when the fault has been corrected.
Important Formula for numerical
- Electricity consumption: PNT
- Electric Power(P): I×V
