{"id":1859,"date":"2020-10-03T20:56:55","date_gmt":"2020-10-03T15:56:55","guid":{"rendered":"https:\/\/murreeroad.org\/physics10\/?p=1859"},"modified":"2020-10-18T23:17:17","modified_gmt":"2020-10-18T18:17:17","slug":"physics-10-chapter14-lq","status":"publish","type":"post","link":"https:\/\/murreeroad.org\/physics10\/physics-10-chapter14-lq\/","title":{"rendered":"Physics 10 Chapter14-lq"},"content":{"rendered":"

<\/a>Chapter 14 Current Electricity\u00a0(Long Questions)<\/strong><\/h2>\n

14.1. Define and explain the term electric current.<\/a><\/strong>
\n14.2. What is the difference between electronic current and conventional current?<\/a><\/strong>
\n14.3. What do we mean by the term e.m.f? Is it really a force? Explain.<\/a><\/strong>
\n14.4. How can we differentiate between e.m.f. and potential difference?<\/a><\/strong>
\n14.5. Explain Ohm’s law. What are its limitations?<\/a><\/strong>
\n14.6. Define resistance and its units.<\/a><\/strong>
\n14.7. What is the difference between conductors and insulators?<\/a><\/strong>
\n14.8. Explain the energy dissipation in a resistance. What is Joule’s law?<\/a><\/strong>
\n14.9. What is difference between D.C and A.C?<\/a><\/strong>
\n14.10. Discuss the main features of parallel combination of resistors.<\/a><\/strong>
\n14.11. Determine the equivalent resistance of series combination of resistors.<\/a><\/strong>
\n14.12. Describe briefly the hazards of household electricity.<\/a><\/strong>
\n14.13. Describe four safety measures that should be taken in connection with the household circuit.<\/a><\/strong>
\n14.14. Design a circuit diagram for a study room that needs the following equipment’s in parallel:<\/a><\/strong>
\n(a) One 100 W lamp operated by one switch.<\/strong>
\n(b) One reading lamp fitted with a 40 W bulb which can be switched ON and OFF from two points.<\/strong>
\n(c) What is the advantage of connecting the equipment’s in parallel instead of series?<\/strong><\/p>\n

CONCEPTUAL QUESTIONS<\/strong><\/p>\n

14.1. Why in conductors charge is transferred by free electrons rather than by positive charges?<\/a>
\n14.2. What is the difference between a cell and a battery?<\/a>
\n14.3. Can current flow in a circuit without potential difference?<\/a>
\n14.4. Two points on an object are at different electric potentials. Does charge necessarily flow between them?<\/a>
\n14.5. In order to measure current in a circuit why ammeter is always connected in series?<\/a>
\n14.6. In order to measure voltage in a circuit voltmeter is always connected in parallel. Discuss. <\/a><\/strong><\/p>\n

14.7. How many watt-hours are there in 1000 joules?<\/a><\/strong>
\n14.8. From your experience in watching cars on the roads at night, are automobile <\/a><\/strong>headlamps connected in series or in parallel.<\/strong><\/a>
\n14.9. A certain flash-light can use a 10 ohm bulb or a 5 ohm bulb. Which bulb should be <\/a><\/strong>used to get the brighter light? Which bulb will<\/a> discharge the battery first?<\/a><\/strong>
\n14.10. It is impracticable to connect an electric bulb and an electric heater in series. Why?<\/a><\/strong>
\n14.11. Does a fuse in a circuit control the potential difference or the current?<\/a><\/a><\/strong><\/p>\n

14.1. Define and explain the term electric current.<\/strong><\/p>\n

Ans. Statement:<\/strong> “The rate of flow of electric charges through cross-section area of a conductor is called electric current”.<\/p>\n

The flowing electric charge may be positive or negative. In case of conducting metal wires the electric current is due to flow of free electrons which carry negative charge.<\/p>\n

Formula: <\/strong>If “Q” denotes the amount of charges flow, through any cross section, in time “t” then value of current “I” is given by I = Q\/t (Ampere)<\/a><\/p>\n

14.2. What is the difference between electronic current and conventional current?<\/strong><\/p>\n

Ans. Electronic current: The current due to negatively charged particles (free electrons) that is from lower potential to higher potential is called electronic current. Conventional current: The current due to positively charged particles that is from higher potential to lower potential is called conventional current.
\nCurrent in metals is electronic current but we take conventional current.<\/a><\/p>\n

14.3. What do we mean by the term e.m.f? Is it really a force? Explain.<\/strong><\/p>\n

Ans. e.m.f. stands for electromotive force. Basically it is the potential energy provided by the source which causes to accelerate the charges (electrons)
\nto move that is current. There is not force but energy.<\/a><\/p>\n

14.4. How can we differentiate between e.m.f. and potential difference?<\/strong><\/p>\n

Ans. e.m.f. is the total amount of energy supplied by the battery or the cell in moving in a one coulomb of positive charge from the negative to positive terminal of the battery, The current passes’ through the external resistor(bulb, appliance) due to which potential drops across it. By Ohm’s law V = IR It is called the potential difference’ across the resistor. e.m.f. is greater than potential difference.<\/a><\/p>\n

14.5. Explain Ohm’s Law. What are its limitations?<\/strong><\/p>\n

Ans. Statement:<\/strong> It states that potential drop (voltage) across a resistance is directly proportional to value of electric current passing through it provided the temperature and the physical state of the conductor does not change.<\/p>\n

Consider V is the potential difference between the two ends of a conductor and I is the current is flowing through it. By ohm’s law we can write:<\/p>\n

Mathematically:<\/strong><\/p>\n

V \u221d I<\/p>\n

V = (Constant) I<\/p>\n

The constant of proportionally is denoted by R called electrical resistance of the conductor, so that<\/p>\n

V = IR \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Mathematical form of Ohm’s law.<\/p>\n

Limitations:<\/strong><\/p>\n

    \n
  1. The temperature of the conductor does not change.<\/li>\n<\/ol>\n

    2. The physical state of the conductor does not change.<\/a><\/p>\n

    14.6. Define resistance and its units.<\/strong><\/p>\n

    Ans. Electrical Resistance :(R)<\/p>\n

    The property of a substance which offers opposition to the flow of current through it is called its resistance,<\/p>\n

    Unit of Resistance: ( Ohm \u03a9)<\/p>\n

    The SI unit of resistance is ohm, its symbol is \u03a9.<\/p>\n

    By Ohm’s law \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 V=IR\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u21d2\u00a0 \u00a0 \u00a0 \u00a0 \u00a0R = V\/I<\/p>\n

    The resistance is said to be one ohm if a potential difference of one volt across the conductor produces an electric current of one ampere through the conductor.<\/a><\/p>\n

    14.7. What is the difference between conductors and insulators?<\/strong><\/p>\n

    Ans. Conductors:<\/strong> Materials offer low resistance to pass current through them are called conductors. For example: AI! metals are good conductors of electricity. Metals have excess of free electrons which are responsible for the flow of current in metals.<\/p>\n

    Insulators:<\/strong> Materials, offer very high resistance and negligible current passes through them, are called insulators.<\/p>\n

    For example:<\/strong> Materials like rubber, glass, wood etc. have not free electrons to move.<\/a><\/p>\n

    14.8. Explain the energy dissipation in a resistance. What is Joule’s law?<\/strong><\/p>\n

    Ans. As a charge\u00a0<\/span>q\u00a0<\/em><\/span>moves through a resistor, it loses a potential energy qV<\/em>\u00a0where\u00a0V<\/em>\u00a0is the potential drop across the resistor. This energy goes into heat, much like the way a ball of putty that falls off a cliff converts its potential energy to heat when it hits the ground. We refer to this conversion of potential energy into heat as\u00a0dissipation<\/strong><\/em>.<\/span><\/p>\n

    The power dissipated in a resistor is the energy dissipated per time. If an amount of charge\u00a0<\/span>D<\/span>t<\/em>\u00a0moves through the resistor in a time\u00a0<\/span>D<\/span>t<\/em>, the power loss is<\/span><\/p>\n

    \"\"<\/p>\n

    where\u00a0<\/span>I<\/strong><\/em><\/span>\u00a0is the current through the resistor and\u00a0<\/span>V<\/strong><\/em><\/span>\u00a0is the voltage drop across it.<\/span><\/p>\n

    The formula\u00a0<\/span>P = I V<\/strong><\/em><\/span>\u00a0also gives the power generated by a battery if\u00a0<\/span>I<\/strong><\/em><\/span>\u00a0<\/strong><\/em><\/span>is the current coming from the battery and\u00a0<\/span>V<\/strong><\/em><\/span>\u00a0is its voltage.<\/span><\/p>\n

    Joule’s Law:<\/strong><\/p>\n

    This\u00a0law<\/b> governs the heating effect of current as heat energy released by a conductor when current passes through it. If the conductor is having resistance R and current I passes through it for time t. The mathematical expression of Joule\u2019s law is as explained below.<\/p>\n

    Q = I2<\/sup>\u00a0R T<\/p>\n

    Where,<\/p>\n