Class 12 Power Chapter 1 Basics Electricity II

Class 12 Power Chapter 1 Basics Electricity II Solutions English Medium As Per AHSEC New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters Class 12 Power Chapter 1 Basics Electricity II Question Answer and select need one. Class 12 Power Chapter 1 Basics Electricity II Notes Download PDF. AHSEC Class 12 Elective Electrical Power System Question Answer English Medium.

Class 12 Power Chapter 1 Basics Electricity II

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Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. AHSEC Class 12 Elective Electrical Power System Textual Solutions are part of All Subject Solutions. Here we have given AHSEC Class 12 Electrical Power System Textbook Solutions English Medium for All Chapters, You can practice these here.

Basics Electricity II

Chapter: 1

1. Explain the following:

(i) Voltage.

Ans: Voltage: The force motivating electrons to “flow” in a circuit is called voltage. The voltage is electrical pressure, a potential force or difference between electrical charges between two points. Voltage pushes the current in a wire. Voltage exists between positive and negative terminals of a battery. Voltage (E or V) is measured in Volts and is abbreviated by the symbol “V”.

One Volt means the force move one coulomb of electrons in one second.

(ii) Current.

Ans: Current: An electric circuit is formed when a conductive path is created to allow electrons to move continuously. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of “flow,” just like the flow of a liquid through a hollow pipe. Current flows in a wire pushed by voltage. Current (I) is measured in Ampere and is designated by the symbol “A”.

Ampere: if one coulomb charge cross over the area of cross section of the conductor per one second then the value of current through the conductor is called ‘One Ampere’.

(iii) Resistance.

Ans: Resistance: Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. The resistance (R) is measured in Ohms and is designated by the symbol “Ω”.

One Ohm – When a conductor having 1 V potential between the two end points, one ampere current will flowing through conductor and the resistance value of conductor is 1 Ohm (Ω).

2. A circuits has two lamps of 100 each 3 tube lights of 40 Watt each, 3 tube lights of 40 watt each, 2 ceiling fans of 80 watt each. Calculate the total wattage? 

Ans:  Given: 2 lamps of 100 W each

3 tube lights of 40 W each

2 ceiling fans of 80 W each

Step 1: Calculate total for each appliance

Lamps: 2 × 100 W = 200 W

Tube lights: 3 × 40 W = 120 W

Ceiling fans: 2 × 80 W = 160 W

Step 2: Add all wattages

Total wattage = 200 W + 120 W + 160 W

 = 480 W

Total Wattage = 480 Watts (W)

3. The smallest particle of an element is known as —

(a) Atom. 

(b) Molecule. 

(c) Nucleus. 

(d) Electron.

Ans: (a) Atom. 

4. The atom is composed of —

(a) Electron only. 

(b) Proton only. 

(c) Neutrons only. 

(d) Electron, Proton, neutrons. 

Ans: (d) Electron, Proton, neutrons.

5. The supply for domestic purpose is —

(a) 110- 120 V. 

(b) 120- 130 V. 

(c) 220- 230 V. 

(d) 400- 440 V.

Ans: (c) 220- 230 V.

6. Tick T if you think the statement is true; Tick F if you think the statement is false.

The signals, which is continuous and can have any value in a limited range, is known as analog signal (T/F)

Ans: True.

Additional:

A. Short Answer Questions:

1. What are the three fundamental particles of an atom, and what are their charges?

Ans: An atom is made up of three fundamental particles:

(i) Protons – have a positive charge (+).

(ii) Electrons – have a negative charge (–).

(iii) Neutrons – have no charge (neutral).

2. Define a conductor, insulator, and semiconductor with one example of each.

Ans: (i) Conductor: Materials that allow electric current to flow easily through them are called conductors.

Example: Copper, Aluminium.

(ii) Insulator: Materials that do not allow electric current to flow are called insulators.

Example: Rubber, Plastic.

(iii) Semiconductor: Materials that have conductivity between a conductor and an insulator are called semiconductors.

Example: Silicon, Carbon.

3. State Ohm’s Law and write its mathematical formula.

Ans: Ohm’s Law states that at constant temperature, the current (I) flowing through a conductor is directly proportional to the voltage (V) across it and inversely proportional to the resistance (R).

Mathematical Formula:

V = I × R

Where: V = Voltage (Volts)

I = Current (Amperes)

R = Resistance (Ohms, Ω)

If voltage increases, current increases (for constant resistance).

4. What is the difference between analog and digital signals?

Ans: The differences between analog and digital signals are:

5. What safety precautions should be taken while working with electricity? List any three.

Ans: To ensure safety while working with electricity, the following precautions must be followed:

(i) Never touch a current-carrying wire or conductor with bare hands.

(ii) Always switch off the supply before checking or repairing any electrical appliance.

(iii) Ensure that proper earthing is provided for all electrical equipment.

B. Long Answer Questions:

1. Explain the atomic structure and its relation to electricity.

Ans: An atom is the smallest particle of any element that still retains the characteristics of that element. Atoms are composed of three types of particles: protons, neutrons, and electrons. The nucleus is at the centre of the atom is made up of positively charged particles called protons and neutrons which are neutral. The nucleus is surrounded by one or more lightweight negatively charged particles called electrons. An atom is held together by forces of attraction between the electrons and the protons. The neutrons help to hold the protons together.

2. What happens when an atom gains or loses electrons? Explain with reference to atoms and electrical charges.

Ans: If an atom has the same number of electrons and protons, it will be balanced and have a neutral charge (no charge). If an atom gains an electron or has more electrons than protons, it will be unbalanced and be negatively charged ion. If an atom loses an electron or has fewer electrons than proton, the atom will be positively charged ion. Positive ions attract electrons from neighbouring atoms to become balanced. This causes electron flow.

3. Define conductors, insulators, and semiconductors, giving examples and reasons for their properties.

Ans: The electrical properties of different materials are governed by the number of electrons in the outer shell –

(i) Conductors: Materials having 1 to 3 electrons in the outer shell makes good conductors. Metals such as copper and aluminium are good conductors of electricity and are used in automobile wiring. The electrical current easily flows in the conductors.

(ii) Insulators: Materials having 5 to 8 electrons in the outer shell are insulators, because the outer shell is almost filled with electrons. Large amount of force is required to free the electrons in these materials. They do not allow the electricity to flow. Glass, rubber, porcelain and plastic are insulators. Electric wires used in automobile are covered with plastic to avoid short circuiting.

(iii) Semiconductors: Materials with exactly 4 atoms in outer shell of the atom are called semiconductors. They are neither good conductors, nor good insulators. Carbon and silicon are semiconductors.

4. What is meant by voltage, current and resistance? Explain each with proper definitions and units.

Ans: (i) Current: An electric circuit is formed when a conductive path is created to allow electrons to move continuously. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of “flow,” just like the flow of a liquid through a hollow pipe. Current (I) is measured in Ampere and is designated by the symbol “A”.

(ii) Voltage: The force motivating electrons to “flow” in a circuit is called voltage. The voltage is electrical pressure, a potential force or difference between electrical charges between two points. Voltage pushes the current in a wire. Voltage exists between positive and negative terminals of a battery. Voltage (E or V) is measured in Volts and is abbreviated by the symbol “V”.

(iii) Resistance: Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. The resistance (R) is measured in Ohms and is designated by the symbol “Ω”.

5. Differentiate between Analog and Digital Electronics and explain their signals.

Ans: 

1. Which one of the following is an active component?

(a) Resistance.

(b) Inductor.

(c) Transistor.

(d) Capacitance.

Ans: (c) Transistor.

2. A milli watt is equal to —

(a) 1/10 watt.

(b) 1/100 watt.

(c) 1/1000 watt.

(d) 1000 watt.

Ans: (c) 1/1000 watt.

3. Which one of the following is not an electromechanical component?

(a) Vibrator.

(b) Relay.

(c) Transformer.

(d) Switch.

Ans: (c) Transformer.

4. In the colour code of resistance in electronic circuits, the tolerance is resented by —

(a) First band.

(b) Second band.

(c) Third band.

(d) Fourth band.

Ans: (d) Fourth band.

5. In the 4-band colour code resistance, the number 2 is indicated by colour —

(a) Red.

(b) Yellow.

(c) Black.

(d) Green.

Ans: (a) Red.

6. The capacitance is measured in —

(a) Henry.

(b) Ohms.

(c) Hertz.

(d) Farads.

Ans: (d) Farads.

7. The capacitance of a parallel plate capacitor will be more if —

(a) Plates have a large area and short distance between plates.

(b) Plates have small areas and large gap between plates.

(c) Small area of plates and high applied voltage.

(d) Large plate area, large plate distance and dielectric of low value.

Ans: (a) Plates have a large area and short distance between plates.

8. Which value of AC current is measured by ammeters?

(a) Peak value.

(b) Average value.

(c) Instantaneous value.

(d) R.M.S. value.

Ans: (d) R.M.S. value.

Additional

A. Short Answer Questions:

1. What are the two main divisions of electronic components?

Ans: Electronic components are divided into two parts –

(i) Passive Component.

(ii) Active Component.

2. What is a resistor?

Ans: The flow of charge (or current) through and material, encounters an opposing force similar in many respects to mechanical friction. This “opposing force” is called the resistance of the material. It is measured in ohms, for which the symbol is “Ω” (the Greek capital letter omega).

3. What is the unit of capacitance?

Ans: The capacitance is measured in units of Farad (F).

4. What is the function of an energy meter?

Ans: An energy meter is an instrument used for recording the energy consumed by a consumer in the form of ‘UNIT’ or ‘KWH’. It is also known as Kilo Watt Hour meter.

5. What is the function of an ammeter?

Ans: An Ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes (A), hence the name is ammeter.

B. Long Answer Questions:

1. Explain the difference between passive and active components with examples.

Ans: (i) Passive Component:- These components are not capable of amplifying or processing an electrical signal.

Resistors, Capacitors, Inductors.

(ii) Active Component: – These components capable of amplifying or processing an electrical signal.

Tube devices, Semiconductor devices.

2. Describe the construction and use of a paper capacitor.

Ans: The basic construction of a paper capacitor is shown in Figure. Since paper can be rolled between two metal foils, it is possible to concentrate a large plate area in a small volume. The capacitor consists of two metal foils separated by strips of paper. This paper is impregnated with a dielectric material such as wax, plastic or oil.

Paper capacitors have capacitance ranging from 0.0005 mF to several mF, and are rated from about 100 V to several thousand volts. They can be used for both dc and ac circuits. Its leakage resistance is of the order of 100 MF.

3. Explain how a full-wave rectifier works.

Ans: In this rectifier circuit, two diodes are used and each one is connected on the two ends of the secondary winding of double winding transformer (center Tapped transformer).

According to the circuit, positive ends of both the diodes are connected with each other. Diode D1 conducts only when positive half cycle comes on its negative end. Similarly, diode D2 conducts only when positive half cycle of AC comes on its negative end. On both of these diodes positive half cycles come alternately which means, when positive half cycles of AC comes on diode D1 then diode D2 gets negative half cycle and when diode D1 gets negative half cycle then diode D2 gets positive half cycle. In this way, diodes D1 & D2 conducts alternately using every half cycle of AC. As a result of this, DC is obtained at the output ends with no gap remaining between the two continuous pulses.

4. What is a transistor and describe its basic parts?

Ans: The Transistor is an electronic device, which is generally made of Semiconductor materials Germanium or silicon.

A transistor is a three terminal device, transistors have three leads, known as base (B), emitter (E), and collector (C). A very small emitter-base current allows a much larger collector-emitter current to flow. Therefore transistors may amplify the signal, or act as a switch.

5. Explain the working and measurement process of a digital multimeter.

Ans: The single meter, by which Voltage(V), Current(A), Resistance(R) and other measurement can be measured, is called the Multimeter. With the help of the multimeter, one can localize troubles (such as short circuits, or open circuits) in the electronic circuitry.

To select the mode of measurement, a “function switch” is provided. By suitably adjusting this switch, the multimeter can be converted into a voltmeter, milli-ammeter, or an ohmmeter. Each position of the switch is labeled accordingly. There is another switch provided, called the “range switch”. Each position of this switch is meant to fix a range of measurements. It is useful to start with the highest range and then switch down to lower ones, until the correct range is reached. This way the instrument is saved from damage due to an exceed current flowing through it. There are two types of multimeter basically use for measurement that is – analog and Digital multimeter but now a day the analog multimeter is out dated and digital multimeter is used.

1. In serial circuit, current is —

(a) Different. 

(b) Same. 

(c) Variable.

(d) Normal. 

Ans: (b) Same.

2. In parallel circuit, voltage is —

(a) Different. 

(b) Same. 

(c) Variable.

(d) Normal. 

Ans: (b) Same.

3. The total resistance of two resistors R1 and R2 when connected in parallel is given by _____________________.

Ans: 1/RT  = 1/R1 + 1/R2.

4. Four capacitors each of 1 µF are connected in parallel. The equivalent total capacitance will be —

(a) 4 µF 

(b) 1 µF 

(c) 0.25 µF 

(d) 2 µF 

Ans: (a) 4 µF.

Additional

A. Short Answer Questions:

1. What is meant by combination of resistances?

Ans: Connecting two resistances to get the required value is known as a combination of the resistances.

2. How many ways can resistances be combined?

Ans: Resistances can be combined in three ways –

(i) Series Combination.

(ii) Parallel Combination.

(iii) Series Parallel Combination.

3. Question: Write the formula for total resistance in a series combination.

Ans: RT = R1 + R2 + R3 + R4 + … Rn.

4. In a series circuit, how does current flow?

Ans: In the series circuit, the current flows in one direction.

5. Write the rule of voltage drop in a parallel circuit.

Ans: The voltage drop is the same in all resistors.

B. Long Answer Questions:

1. Explain series combination of resistances with formula and example.

Ans: When one end of a resistance is connected to one end of a second resistance and other end of second resistance is connected to the end of third resistance, then this combination is known as series combination. In this combination, the total resistance of the combination is the sum total of the resistance used in it and the total wattage is the wattage of a single resistance. If resistances of different watts are used then the total wattage will be the wattage of lowest wattage resistance used. According to the figure, Total value = 10 + 20 + 50 = 80 Ω. Formula: RT = R1 + R2 + R3 + R4 + … Rn. Example: Two resistances, each of 2 Ω and a resistance 4 Ω are connected in series. Calculate the total resistance of the combination. If supply of 40 V is given to this circuit, then calculate the total current. RT = R1 + R2 + R3 = 2 + 2 + 4 = 8 Ω. Since VT = 40 V & RT = 8 Ω, I = 40 / 8 = 5 Amp. Thus, 5 Amp of current will flow in the circuit on giving supply of 40 V.

2.  Explain parallel combination of resistances and write its formula.

Ans: In parallel combination, two or more resistances are connected across the same voltage source. In this condition, each resistance makes a different path for current flow. In this way, voltage across all the resistances is equal to the voltage capacity of the voltage source. This is just opposite of the series circuit, where current remains and voltage drops according to the value of resistance. Different wattage resistance can be used in the parallel combination. Hence, total wattage of the combination is equal to the sum total of all the wattage of the resistances and equivalent resistance of the parallel combination can be found by the formula given below:

1/RT = 1/R1 + 1/R2 + 1/R3 + 1/R4 +……

3. Question: Write important rules of a series circuit.

Ans: (i) In the series circuit, the current flows in one direction.

(ii) Total Resistance R = R1 + R2 + R3 + …

(iii) In a series circuit, the same current passes through all its resistors.

(iv) The total drop across the series circuit is the sum of voltage drop across each resistor.

(v) The total series circuit will be inactive (there is no current flow) there is a fault in any one of its resistors.

(vi) This type of connection is used in serial sets (Decorative lamps).

4. Question: Write important rules of a parallel circuit.

Ans: (i) In the parallel circuit current flows through two or more paths at a junction. That is, it gets divided.

(ii) The voltage drop is the same in all resistors.

(iii) If there are 3 resistors (R1, R2, R3) in circuit 1/R = 1/R1 + 1/R2 + 1/R3.

(iv) If there is a fault in one resistor the other two resistors will work. The current will be divided into two parts and will flow through the two resistors.

5. Question: Explain series-parallel circuit with example.

Ans: In this circuit one and more resistors connected in series with one more resistor connected in parallel. It is a combination of series and parallel circuit. In the above series parallel circuit there are five resistors (R1, R2, R3, R4, R5) placed in it among them R1, R2 are connected in series and R3, R4, R5 are connected in parallel. The parallel resistors are connected in series with R1 and R2. Example: 10 Ω and 8 Ω resistors are connected in parallel with a 4 Ω resistor in series. Find out the total resistance of the series parallel circuit. Resistance of the parallel circuit = 2.4 Ω. Total resistance of the series parallel circuit R = 8 Ω.

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