Tanveer Kurd Books

Skip to content Physics10 According to Syllabus (Test Your Skill) TOGGLE NAVIGATION Chapter 16 Basic Electronics (Long Questions) 16.1. Describe, using one simple diagram in each case, what happens when a narrow beam of electrons is passed through (a) a uniform electric field (b) a uniform magnetic field. What do these results indicate about the charge on electron? 16.2. Explain the working of different parts of oscilloscope. 16.3. Name some uses of oscilloscope. 16.4. Considering an oscilloscope explain: (i) How the filament is heated? (ii) Why the filament is heated? (iii) Why the anode potential is kept positive with respect to the cathode potential? (iv) Why a large potential is applied between anode and cathode? (v) Why the tube is evacuated? 16.5. What is electron gun? Describe the process of thermionic emission. 16.6. What do you understand by digital and analogue quantities? 16.7. Differentiate between analogue electronics and digital electronics. Write down names of five analogue and five digital devices that are commonly used in everyday life. 16.8. State and explain for each case whether the information given by the following devices is in analogue or a digital form. a. a moving-coil voltmeter measuring the e.m.f of a cell. b. a microphone generating an electric current. c. a central heating thermostat controlling the water pump. d. automatic traffic lights controlling the flow of traffic. 16.9. Write down some benefits of using digital electronics over analogue electronics. 16.10. What are the three universal Logic Gates? Give their symbols and truth tables. CONCEPTUAL QUESTIONS 16.1. Name two factors which can enhance thermionic emission. 16.2. Give three reasons to support the evidence that cathode rays are negatively charged electrons. 16.3. When electrons pass through two parallel plates having opposite charges, they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this? 16.4. When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection. 16.5. How can you compare the logic operation X=A.B with usual operation of multiplication? 16.6. NAND gate is the reciprocal of AND gate. Discuss 16.7. Show that the circuit given below acts as OR gate. 16.8. Show that the circuit given below acts as AND gate. 16.1. Describe, using one simple diagram in each case, what happens when a narrow beam of electrons is passed through (a) a uniform electric field (b) a uniform magnetic field. What do these results indicate about the charge on electron? Ans. (a) A uniform Electric Field: When an electron beam is passed through a uniform electric field it deflects and accelerates the electron beam as shown in figure. (b) A uniform Magnetic Field: When an electron beam is passed through a uniform magnetic field it only deflects the electron beam. The two above results show that electrons carry negative charge. 16.2. Explain the working of different parts of oscilloscope. Ans. The CRO stands for a cathode ray oscilloscope. It is typically divided into four sections which are display, vertical controllers, horizontal controllers, and Triggers. Most of the oscilloscopes are used the probes and they are used for the input of any instrument. We can analyze the waveform by plotting amplitude along with the x-axis and y-axis. The applications of CRO’s mainly involve in the radio, TV receivers, also in laboratory work involving research and design. In modern electronics, the CRO plays an important role in the electronic circuits. 16.3. Name some uses of oscilloscope. Ans. Uses: Cathode ray oscilloscope is a versatile electrical instrument which is in fact a high speed graph plotting device. 1. Voltage Measurement: Enter the unknown voltage at “Y -input” and the “VOLT/DIV” knob at the oscilloscope can be tuned to be used as voltmeter. 2. Time Measurement: By adjusting the “TIME/DIV” knob the oscilloscope can be used to measure the time. 3. To show the x-t signal: Oscilloscope can display the time signal (voltage-time or current-time) output whether it can be shown in beat high frequency wave. 4. To show the x-y graph: The relation between two variables can be displayed by entering a horizontal signal and vertical signal. 16.4. Considering an oscilloscope explain: (i) How the filament is heated? (ii) Why the filament is heated? (iii) Why the anode potential is kept positive with respect to the cathode potential? (iv) Why a large potential is applied between anode and cathode? (v) Why the tube is evacuated? Ans. i. Filament is heated by a battery usually of 6 Volts. ii. Filament is heated to get the electrons by thermionic emission. iii. The anode potential is positive with respect to the cathode because electrons being negatively’ charged particles are accelerated towards the anode (positive potential). iv. The degree of deflection and acceleration produced in electrons is proportional to the strength of the electric field. So high potential will accelerate the electrons to high speed and they shoot straight through the hole of the anode in a fine beam of electrons. v. The tube is evacuated because electrons could not collide with other gas to give rise other electrons and ions. 16.5. What is electron gun? Describe the process of thermionic emission. Ans. Electron Gun: Electron gun is an important mean to provide continuous beam of electrons. It consists of a evacuated glass tube at a very low pressure. The electrons are produced by thermionic emission from a tungsten filament heated by a battery, usually 6 V supply. A high positive potential (several thousands) is applied to cylindrical anode (+). The electrons will be accelerated to a high speed and they shoot straight through the hole of the anode in a fine beam of electrons. 16.6. What do you understand by digital and analogue quantities? Ans. (1) Analogue Quantities: The analogue quantities are those whose values vary continuously. For example the variation of temperature with time during a day is shown by the help of a graph shown below. This shows that temperature variation with time is continuous. So we can say that temperature is an analogue quantity with respect to time. Similarly, pressure, distance covered by a moving car etc. are all analogue physical quantities. Digital Quantities: The Part of electronics which processes the data provided in the form of digits or numbers is known as “digital electronics”. Digital electronics uses only two numbers 1 (high) and 0 (low), the whole data is provided in binary system due to which processing has become very easy. 16.7. Differentiate between analogue electronics and digital electronics. Write down names of five analogue and five digital devices that are commonly used in everyday life. Ans. Analogue Electronics: The section of electronics, which is concerned with circuits processing analogue quantities like current, voltage etc. is called analogue electronics. Digital Electronics: Digital electronics use the digital signal In a sequence of voltage pulses represented in binary digits “0” and “1”. Computer operates by counting the digits, Five Analogue Devices: (l)Refrigerators (2) Electric fans (3) Electric iron (4) Electric lamps (5)Radio receiver. Five Digital Devices: (1) Computer (2) T.V. (3) Digital camera (4) Mobile (Cell) phone (5)Security system 16.8. State and explain for each case whether the information given by the following devices is in analogue or a digital form. a. a moving-coil voltmeter measuring the e.m.f of a cell. b. a microphone generating an electric current. c. a central heating thermostat controlling the water pump. d. automatic traffic lights controlling the flow of traffic. Ans. a. It is analogue device which measure the value of e.m.f of a cell. The deflection of the moving-coil is continuous variation with time. It is analogue signal. b. A public address system shown in figure below is an example of analogue electronic system. The microphone converts sound energy into continuously varying voltage/current. It is called analogue voltage/current signal. This signal is applied to an amplifier; which is also analogue electronic circuit, which amplifies the signal without changing its shape, which operates the loud speaker. c. Thermostat controlling the flow of traffic. The thermostat ‘depends upon the atmospheric temperature which vanes continuously with time. It is an analogue signal. So the thermostat controlling the flow of traffic is an analogue device. d. Automatic traffic lights controlling the flow of traffic. It is an digital system which is being operated between two values” 1″ high (Present) and 10w”O” (Not present). 16.9. Write down some benefits of using digital electronics over analogue electronics. Ans. Digital electronics use the digital signal in a sequence of voltage pulses represented in binary digits “O” and “I”. Computer operates by counting the digits. The process with numbers becomes fast, reliable and less error as compared to analogue signal. Digital electronics is being used in every modem electronic device like modern telephone system, radar system, naval and other military controlling systems, modern cameras,’ control system of operation of industrial machines, medical equipf!1ent etc. 16.10. What are the three universal Logic Gates? Give their symbols and truth tables. Ans. AND, OR and NOT are the three universal Logic Gates. The AND Gate In Boolean Algebra the AND function is the equivalent of multiplication and so its output state represents the product of its inputs. The AND function is represented in Boolean Algebra by a single “dot” (.) so for a two input AND gate the Boolean equation is given as: Q = A.B, that is Q equals both A AND B. The 2-input Logic AND Gate The OR Gate In Boolean Algebra the OR function is the equivalent of addition so its output state represents the addition of its inputs. In Boolean Algebra the OR function is represented by a “plus” sign (+) so for a two input OR gate the Boolean equation is given as: Q = A+B, that is Q equals either A OR B. The 2-input Logic OR Gate The NOT Gate The NOT gate, which is also known as an “inverter” is given a symbol whose shape is that of a triangle pointing to the right with a circle at its end. This circle is known as an “inversion bubble”. The NOT function is not a decision making logic gate like the AND, or OR gates, but instead is used to invert or complement a digital signal. In other words, its output state will always be the opposite of its input state. The NOT gate symbol has a single input and a single output as shown. The Logic NOT Gate CONCEPTUAL QUESTIONS 16.1. Name two factors which can enhance thermionic emission. Ans. Thermionic Emission depends upon: The substance used as filament because different materials have different number of free available electrons. The value of the battery used to make it heated. 16.2. Give three reasons to support the evidence that cathode rays are negatively charged electrons. Ans. 1. The cathode rays are deflected and accelerated towards’ positively charged plate . 2. The deflection of cathode rays is the presence of magnetic field shows. that these are negatively charged particles. 3. Grid in the oscilloscope is negatively charged and the electrons are repelled by the. grid It shows that cathode rays (electron beam) is negatively charged particles. 16.3. When electrons pass through two parallel plates having opposite charges, they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this? Ans. If electrons will deflect towards the positive charged plate it means electrons are negatively charged particles. 16.4. When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection. Ans. Fast moving electrons pass through magnetic field, they are deflected from their straight path shows that these are charged particles. The deflection can be enhanced by increasing the velocity and magnetic field strength. 16.5. How can you compare the logic operation X=A.B with usual operation of multiplication? Ans. There is logic operation which is give by the equation (X = A.B). It is called AND gate. This particular gate holds the usual operation of multiplication. The truth table of this gate is given below. 16.6. NAND gate is the reciprocal of AND gate. Discuss Ans. NAND gate is not reciprocal of AND gate. We can say that NAND gate is inversion of AND gate. If X is output of NAND gate then mathematically we can write as 16.7. Show that the circuit given below acts as OR gate. Ans. Yes it acts the OR gate. If X is output of the circuit shown above then mathematically We can write as Its truth table is given. below. A B 0 0 1 0 1 0 0 1 0 1 0 1 1 1 0 1 16.8. Show that the circuit given below acts as AND gate. Ans. Yes, it acts as AND gate. If X is output of the circuit shown above then mathematically we can write as Its truth table is given below. A B 0 1 0 1 1 1 0 0 1 0 0 1 1 0 0 1 0 1 0 0 Go to Top Skip to content Physics10 According to Syllabus (Test Your Skill) TOGGLE NAVIGATION Chapter 15 Electromagnetism (Long Questions) 15.1. Demonstrate by an experiment that a magnetic field is produced around a straight current-carrying conductor. 15.2. State and explain the rule by which the direction of the lines of force of the magnetic field around a current-carrying conductor can be determined. 15.3. You are given an unmarked magnetized steel bar and bar magnet, its north and south ends are marked N and S respectively. State how would you determine the polarity at each end of the unmarked bar? 15.4. When a straight current-carrying conductor is placed in a magnetic field, it experiences a force. State the rule by which the direction of this force can be found out. 15.5. State that a current-carrying coil in a magnetic field experiences a torque. 15.6. What is an electric motor? Explain the working principle of D.C motor. 15.7. Describe a simple experiment to demonstrate that a changing magnetic field can induce e.m.f. in a circuit. 15.8. What are the factors which affect the magnitude of the e.m.f. induced in a circuit by a changing magnetic field? 15.9. Describe the direction of an induced e.m.f. in a circuit? How does this phenomenon relate to conservation of energy? 15.10. Draw a labelled diagram to illustrate the structure and working of A.C generator. 15.11. What do you understand by the term mutual induction? 15.12. What is a transformer? Explain the working of a transformer in connection with mutual induction. 15.13. The voltage chosen for the transmission of electrical power over large distances is many times greater than the voltage of the domestic supply. State two reasons why electrical power is transmitted at high voltage. 15.14. Why is the voltage used for the domestic supply much lower than the voltage at which the power is transmitted? CONCEPTUAL QUESTIONS 15.1. Suppose someone handed you three similar iron bars and told you one was not magnet, but the other two were. How would you find the iron bar that was not magnet? 15.2. Suppose you have a coil of wire and a bar magnet. Describe how you could use them to generate an electric current. 15.3. Which device is used for converting electrical energy into mechanical energy? 15.4. Suppose we hang a loop of wire so that it can swing easily. If we now put a magnet into the coil, the coil will start swinging. Which way will it swing relative to the magnet, and why? 15.5. A conductor wire generates a voltage while moving through a magnetic field. In what direction should the wire be moved, relative to the field to generate the maximum voltage? 15.6. What is the difference between a generator and a motor? 15.7. What reverses the direction of electric current in the armature coil of D.C motor? 15.8. A wire lying perpendicular to an external magnetic field carries of a current in the direction shown in the diagram below. In what direction will the wire move due to the resulting magnetic force? 15.9. Can a transformer operate on direct current? 15.1. Demonstrate by an experiment that a magnetic field is produced around a straight current-carrying conductor. Ans. Current carrying conductors in opposite directions. In both cases, the current carrying conductor is intercepted by a cardboard placed at right angles to the current carrying conductor. There are some iron fillings sprinkled on the conductor. When current flows through the conductor, the iron filing arrange themselves along the magnetic field. We can see that the magnetic field in both cases is in opposite directions as is the current. The magnetic field produced by a current-carrying straight wire depends inversely on the distance from it and directly on the current passing through it. From this we see that the current carrying conductor produces a magnetic field around it. The direction of this magnetic field is given by Right Hand Thumb Rule. Right Hand Thumb Rule Suppose that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of flow of current. Then, your fingers which wrap around the conductor indicate the direction of magnetic field lines (as shown in the figure) 15.2. State and explain the rule by which the direction of the lines of force of the magnetic field around a current-carrying conductor can be determined. Ans. Right hand rule is used to determine the direction of a magnetic field lines relative to the direction of conventional current. “Grasp the straight conductor in our right-hand with the stretched thumb along the direction of the conventional (positive) current. The curling finger of the hand will point in the direction of the magnetic field. Right hand grip rule 15.3. You are given an unmarked magnetized steel bar and bar magnet, its north and south ends are marked N and S respectively. State how would you determine the polarity at each end of the unmarked bar? Ans. Bring the north pole of bar magnet near one end (1st face) of unmarked magnetized steel bar. If they attract each other, then this face of steel bar is south pole. If they repel each other, then this face of steel bar is north pole. Mark this face with north or south accordingly and repeat the above exercise to mark the 2nd face of magnetized steel bar. 15.4. When a straight current-carrying conductor is placed in a magnetic field, it experiences a force. State the rule by which the direction of this force can be found out. Ans. The direction of the force on a current-carrying conductor is determined by the Fleming’s left hand rule. Fleming’s Left Hand Rule: It states that “Stretch the thumb, forefinger and the middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger in the direction of the current, then the thumb would indicate the direction of the force acting on the conductor. 15.5. State that a current-carrying coil in a magnetic field experiences a torque. Ans. If a coil carrying a current is placed in a magnetic field it will experience a force on two of its sides in such a way as to make the coil rotate. This effect is the basis of all electric motors and moving coil meters. Think of all the places where electric motors are used from stereos, disc drives, CD players, starter motors in cars, washing machines etc. etc. and you will realize how important this effect is? The forces are shown in Figure. You can see why the coil will rotate from the ‘double catapult’ field diagram in Figure (b). Since the current moves along the two opposite sides of the coil in opposite directions the two sides receive a force in opposite directions also, thus turning the coil. Mathematical consideration Formulae for the force on a coil in a magnetic field Consider a rectangular coil with sides of length a and b placed in a magnetic field of flux density B and free to rotate about an axis perpendicular to the paper, current of I Amps flows in the coil. The field exerts a force on the sides b given by Force (F) on side length b = BNIb where N is the number of turns on the coil. If the perpendicular to the coil is at an angle θ to the field direction, then the torque exerted on the coil is Fd where d = a sin q. Therefore the torque C is given by: Torque (C) on the coil = Fa sinθ = BNIba sin θ or: Torque (C) on the coil = BANI sinθ where A = ab, the area of one face of the coil. The maximum torque occurs when the plane of the coil is lying along the field lines (θ = 90o and sin q = 1). At this point, shown in Figure (a). Maximum torque (Co) = BANI The minimum value of the torque is zero, when θ = 0. 15.6. What is an electric motor? Explain the working principle of D.C motor. Ans. An electric motor is an electrical machine that converts electrical energy into mechanical energy. General-purpose motors with standard dimensions and characteristics provide convenient mechanical power for industrial use. Working principle of D.C motor A current-carrying conductor will experience a force when placed within a magnetic field. The principle of the electric motor is that it converts electrical energy into kinetic energy (mechanical energy) through the interaction of the two magnetic fields. A simple DC motor uses a stationary set of magnets in the stator, and a coil of wire with a current running through it to generate an electromagnetic field aligned with the center of the coil. The commutator allows each armature coil to be energized in turn, creating a steady rotating force (known as torque). 15.7. Describe a simple experiment to demonstrate that a changing magnetic field can induce e.m.f. in a circuit. Ans. When a magnet is pushed into the solenoid, there is a change in magnetic field lines linking the solenoid, which produces an induced e.m.f. This induced e.m.f. drives a current in the circuit, causing the pointer of the galvanometer deflects momentarily. When the magnet is stationary, there is no change in magnetic field lines linking the circuit. There is no induced e.m.f. and hence no current detected by the galvanometer. The experiment show that induced current (or induced emf) is produced in the coil due to the changing magnetic field in the solenoid. This process is called electromagnetic induction. The factors affecting the magnitude of the induced emf can be demonstrated as follows: a. When the magnet moves at a faster speed in or out of the coil, the magnitude of the induced current is increased. b. When a stronger magnet is used, the magnitude of the induced current is increased. c. When the number of turns in the coil is increased, the magnitude of the induced current is increased. 15.8. What are the factors which affect the magnitude of the e.m.f. induced in a circuit by a changing magnetic field? Ans. Factors: Following are the factors which affect the magnitude of the induced emf in a circuit. Speed of relative motion of the coil and the magnet. Number of turns and area of cross-section of the coil. Amount of current passing through the coil. 15.9. Describe the direction of an induced e.m.f. in a circuit? How does this phenomenon relate to conservation of energy? Ans. The direction of induced emf and induced current is determined by Len’s law which states. The direction of the induced current is always such that it opposes the cause that produces it. The induced emf is produced by the changing of magnetic flux in the circuit. The magnetic flux is changed by applying mechanical energy. So one kind of energy is going to change into electrical energy. Hence this phenomenon is in accordance with the conservation of energy. 15.10. Draw a labelled diagram to illustrate the structure and working of A.C generator. Ans. A simple AC generator consists of a rectangular coil ABCD which can be rotated rapidly between the poles N and S of a strong horseshoe-type permanent magnet M. The two ends A and D of the coil are connected to two circular pieces of copper metal called slip rings R1 and R2 15.11. What do you understand by the term mutual induction? Ans. Mutual-induction: The phenomenon of production of induced emf in one coil due to change of current in a neighboring coil is called mutual induction. The SI unit of mutual induction is “Henry”. Its mathematical form is given as M = – (emf)s * Δt/ΔIp Negative sign is the due to Len’s Law. Where “M” stands for mutual induction, S for secondary coil across which emf is being generated due to rate of change of current in primary (P) coil. Henry: The mutual inductance of two coils is said to be one “Henry”. If a current changes at the rate of one ampere per second in the primary causes an induced emf of one volt in the secondary coil. 15.12. What is a transformer? Explain the working of a transformer in connection with mutual induction. Ans. Transformer: The transformer is a practical application of mutual induction. Transformers are used to increase or decrease AC voltages. Usage of transformers is common because they change voltages with relatively little loss of energy. In fact, many of the devices in our homes, such as game systems, printers, and stereos use transformers for their working. Working of a transformer A transformer consists of two electrically isolated coils and operates on Faraday’s principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding. Vs/ Vp = Ns/Np If the secondary voltage is larger than the primary voltage, the transformer is called a step-up transformer. (Fig (a)) If the secondary voltage is smaller than the primary voltage, the transformer is called a step-down transformer. (Fig (b)) In an ideal transformer, the electric power delivered to the secondary circuit is equal to the power supplied to the primary circuit. An ideal transformer dissipates no power itself, and for such a transformer, we can write: Pp = Ps Vp Ip = Vs Is 15.13. The voltage chosen for the transmission of electrical power over large distances is many times greater than the voltage of the domestic supply. State two reasons why electrical power is transmitted at high voltage. Ans. Electric power of transmission is the bulk movement of electrical energy from power station to electrical substation. Power is transmitted at higher voltage to reduce power losses during transmission. Power is the product of voltage and current. P = VI I = P/V So when the same amount of power is transmitted at high voltages, current in the conductor should be low. This leads to less power loss in the power lines. Since power loss is proportional to the square of current. P = I2R So, for the same value of R and Power, Power losses is less if current is less this can be achieved by transmitting power at high voltages. 15.14. Why is the voltage used for the domestic supply much lower than the voltage at which the power is transmitted? Ans. The voltage used for the domestic supply are much low.er because voltage is stepped down and is transmitted to the city sub-station. All the house- hold appliances operate on 220V. CONCEPTUAL QUESTIONS 15.1. Suppose someone handed you three similar iron bars and told you one was not magnet, but the other two were. How would you find the iron bar that was not magnet? Ans. There are two methods to identify that which iron bar is not magnetic. Method-I Having three similar iron bars in hand bring them close to each other one by one and from both ends separately. The iron bars will being attracted but not repelled by any end of the others two bars. This will be the iron bar. Method-II Having three similar iron bars in hand bring them close to a compass needle one by one. In case of magnetic bar the compass needle will det1ect due to the presence of other magnetic field but there is no deflection in case of iron bar. 15.2. Suppose you have a coil of wire and a bar magnet. Describe how you could use them to generate an electric current. Ans. From figure this is called as Faraday’s laws of electromagnetic induction which states that when a magnetic flux linked with the coil changes, there’s an emf that is induced in the coil. Now if you want to generate electricity, just move the magnet in and out at a regular interval and you will see the coil of galvanometer is moving which means electricity is produced. If instead of this galvanometer, you connect an LED, it will glow; maybe dimmer than what you expect but electricity will be produced. 15.3. Which device is used for converting electrical energy into mechanical energy? Ans. A device which converts electrical energy into mechanical energy is called an electrical motor. The working principle of an electric motor depends on the magnetic and electric field interaction. 15.4. Suppose we hang a loop of wire so that it can swing easily. If we now put a magnet into the coil, the coil will start swinging. Which way will it swing relative to the magnet, and why? Ans. The loop will swing fro) having the magnet at mean position.