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    NEET Study Notes for Current Electricity, Important Formulas and Solved Sample Questions

    Nikkil Visha Nikkil Visha
    Exams Prep Master

    Current Electricity is a field of physics which deals with current, flow of current, resistance of a conductor, electric energy and related concepts. It is one of the main topics of NEET exams and is a very easy topic to score, if prepared thoroughly. To help students prepare for NEET exam, we are providing students with revision notes on Current Electricity which consists of important concepts, formulas, and some tips and tricks to solve current electricity questions.

    • There are 3-4 questions from this topic in NEET exam and each question carries 4 marks each.
    • The weightage of this entire topic is around 4-5% of NEET.
    • Some of the important sub topics includes electric current, Ohm’s Law, Resistance of different materials etc.

    We have also added some quick notes of current electricity and its sub-topics so that you can quickly cover all the necessary points. Along with this, sample questions of each sub-topics and previous year solved questions are also given in the article.

    Must Read:

    What is Electric Current?

    Electric Current

    Electric current is defined as the rate (t) of flow of charges(q) through any cross section in a conductor. It is scalar quantity and its SI unit is Ampere(A).

    If the flow of charge is uniform, then,

    Electric Current (i) = q/t = ne/t

    If the flow of charge is non- uniform, then,

    Electric Current (i) = dq/dt or q=? I dt

    Different units of electric current are:

    1. SI unit- Ampere(A) – 1 Ampere= 1 coulomb/ 1 second
    2. CGS electro static unit (esu)- 1 esu of current (stat-ampere) = 1 esu of charge/ 1 second
    3. CGS electro static unit (emu) – 1 emu of current (ab ampere) = 1 emu of charge/ 1 second
    4. 1 A= 3 x 109 esu of current
    5. 1 A= 1/10 emu of current

    Sample Questions

    Question: The electric current (i) in the circuit given below is?

    1. a) (1/45) ampere
    2. b) (1/15) ampere

    (c) (1/5) ampere

    (d) (1/10) ampere

    Answer: (d)


    Ohm’s Law of Conductors

    Ohm’s Law of Conductors

    Ohm’s Law of conductors states that a current flowing through a conductor of uniform area of cross-section at a constant temperature is proportional to the difference of potential across its terminals.

    Important equations of Ohm’s Law:

    1. V= IR
    2. I= V x R
    3. R=ρl/A
    4. ρ= 1/σ
    5. ρ = m/ne2
    6. Vd = (qE /m)
    7.  I = neAvd
    8. σ = ne2 /m

    Here V= Voltage, I= current and R= Resistance.

    Sample Question:

    Question: In the given circuit below, current flowing through a 5 ohm resister produces 10 calories of heat per second. Find the heat generated in 4 ohm resister:

    1. calorie/sec
    2. calorie/sec
    3. calorie/sec
    4. calorie/sec

    Answer: (b)


    Drift Velocity & Resistance

    Drift Velocity

    Drift Velocity is the velocity through which free electrons are drifted towards positive terminal under the action of the applied field.

    V= (eV/ ml)

    Here e= Charge of electron, V= potential difference, m= mass and = relaxation time.

    Relation between current electricity and drift velocity:

     I= q/t= nAve

    Resistance

    The ration between potential differences between the two ends of the conductor to the current flowing through it is called as the resistance(R) of a conductor.

    R= V/I

    Units of Resistance (R)

    1. SI unit- Ohm- 1 Ohm= 1 volt/ 1 ampere
    2. CGS system- 1statohm = 1 statvolt/1 statamp

    -1 abohm = 1 abvolt/1 abampere

    1. 1 Ohm= 1/9 x 1011 statohm
    2. 1 Ohm = 109 abohm

    Variation of Resistance with Temperature

    A change in the resistance of the conductor per unit resistance per degree centigrade rise of temperature is defined as Temperature Coefficient of Resistance (α).

    1. Rt=R0[1+α(T-T0)]
    2. α = Rt - R0/R0(T-T0)

    Here R0, Rt is the resistance of the conductor at 0º C and tº C respectively.

    Sample Question

    Question: What will be the resistance of a wire, if a wire is is stretched to make 0.1% longer?

    1. Decrease 0.05%
    2. Decrease 0.2%
    3. Increase 0.2%
    4. Increase 0.05%

    Answer: (3)

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    Faraday’s Law of Electrolysis

    Faraday’s Law of Electrolysis

    According to Faraday’s Law of Electrolysis,

    (a). Mass of an ion deposited on an electrode during the process of electrolysis is proportional to the quantity of charge that has passed through the electrolyte, i.e,

    m= Zq= Zlt

    (b). When same current passes through several electrolytes at the same time, then, the masses of various ions deposited at each of the electrodes are proportional to their chemical weights, i.e,

    m/W= constant

    or, Z1/Z2= W1/W2

    Thus, W/Z= constant= F


    Resistance in a Series & Parallel

    Resistance in a Series and Resistance in a Parallel

    Resistance in a series: According to this, if a number of resistances are connected in a series with each other, then the net resistance of the combination is equal to their individual resistances.

    1. R = R1+ R2+ R3
    2. V = V1+ V2+ V3
    3. V1 = IR1, V2 = IR2, V3 = IR3
    4. I = I1 = I2 = I3 = Constant

    Resistance in a Parallel: According to this, if a number of resistances are connected in parallel, then the reciprocal of the resistance of combination is equal to the sum of the reciprocals of their individual resistances, i.e,

    1. 1/R = 1/ R1 + 1/ R2 +1/ R3
    2.  I = I1+I2+I3
    3. I1 = V/R1, I2 = V/R2, I3 = V/R3
    4.  V = V1 = V2 = V3 = Constant

    Distribution of current in a parallel combination of resistances:

    1. I2 = I (R1/R1+R2)
    2. I1 = I (R2/R1+R2)

    In general, it means, that current in one branch = total current x (resistance of second branch/sum of resistances of both branches).

    Sample Questions

    Question: Given below are 3 resistances of equal value arranged in different combinations. Arrange them in increasing order of power dissipation.

    1. III
    2. I
    3. II
    4. I

    Answers: (a)

    Important Topics in Current Electricity

    While Current electricity in itself is an important topic to prepare while preparing for JEE Main exam, it also has several important sub-topics which needs to be prepared with due diligence. Some of these topics are mentioned below:

    • Electric Current
    • Drift Velocity
    • Ohm’s Law
    • Electrical Energy and Power
    • Resistance of different Materials
    • Units of Resistance
    • Electrical Resistivity
    • Variation of resistivity
    • Current Density
    • Faraday’s Law of Electrolysis
    • Kirchoff’s Law
    • Temperature dependence of Resistors
    • Series and Parallel Combinations of Resistors
    • Electromotive Force and Potential Difference
    • Electrical Cell and its internal resistance

    Previous Year Sample Questions

    Previous Year Solved Sample Questions

    Question: Find the value of constant along the length of the conductor. Considering a steady current is flowing in a metallic conductor which has a non-uniform cross-section.

    1. a) current, electric field and drift speed
    2. b) drift speed only
    3. c) current and drift speed
    4. d) current only

    Answer: (d)

    Question: What will be the minimum capacity of the main fuse of the building if, there are

    • 15 bulbs of 40 W
    • 5 bulbs of 100 W
    • 5 fans of 80 W
    • 1 heater of 1 kW
    1. 14 A
    2. 12 A
    3. 10 A
    4. 8 A

    Answer: (2)

    Question: Find the incorrect statement:

    1.  Kirchhoff’s second law represents energy conservation.
    2. In a balanced wheat stone bridge if the cell and the galvanometer are exchanged, the null point is disturbed.
    3. A rheostat can be used as a potential driver.
    4. Wheatstone bridge is the most sensitive when all the four resistances are of the same order of magnitude.

    Answer: (2)

    Question: If on interchanging the resistances, balance point of a meter bridge shifts to the left by 10 cm and the resistance of the series is 1k Ω, then find the resistance on the left before interchanging the resistances.

    1. 505 k Ω
    2. 900 k Ω
    3. 550 k Ω
    4. 920 k Ω

    Answer: (3)

    Question: If two bulbs of 25W-220V and 100W-220V are connected in a series of 440V supply then which of these bulbs will fuse?

    1. 100W
    2. 25W
    3. Both
    4. Neither

    Answer: (2)

    Question: Find the tolerance of the combination if 400 Ω of resistance is made by adding four 100 Ω resistance of tolerance 5%.

    1. 5%
    2. 20%
    3. 15%
    4. 10%

    Answers: (1)

    Download NEET Practice Papers

    Some Tips & Tricks to Solve Questions

    Some tips and tricks to solve the NEET paper are given below:

    1. On exam day, Start by attempting easy questions.

    Since you are time bound, go through all the questions in the beginning and then start by solving the easy questions first, then moderate level questions and if time permits then difficult questions. Thus, you will be able to solve more questions in limited time.

    1. Start giving mocks at the same time of exam

    Since the date and time of the examination is available, you can start making your schedule according to the day of exam. Start giving mock tests at the same time at which you have exam on the D-Day. This will help you body and mind ready for the exam day.

    1. Read questions carefully

    On the exam day, read questions twice and then look at the options carefully. Since it is a MCQ paper, elimination method could be applied in some options and thus will save you a lot of time.

    1. Put Values to narrow down your options

    In some questions, equations will be given in options. Solving these equations and checking each of them consumes a lots of time. Try solving them by putting numbers, this saves your time and narrows down your options too.

    1. Do Not panic

    Stay calm and focussed and do not panic if you can’t solve one question. Breathe in, relax and solve next one, and come back to it later on, if you have time.

    Study Plan

    Since less than 1 month or 30 days is left for NEET 2020, most of you guys would be done with their syllabus, and would be doing revision these days. So here we provide you with a quick revision plan to cover all necessary topics and some do’s and don’ts to help you within this short span of time:

    • Make a checklist of all-important formulas, and revise/ read all of them regularly twice a day. You can revise them once after w2aking up in the morning and once at night before going to bed. It will take only 10-15 minutes but will give you a quick revision.
    • Since most of you will be attempting mocks these days, analysing these mocks is a very crucial step. After attempting mock tests, analyise them and re-solve unattempted or wrong attempted questions.
    • You can also try attempting previous year question papers and this year’s sample papers.
    • Don’t try any new topics now, just revise previous topics thoroughly.
    • Do not attempt any mock tests, in the last week before exam. Just go through your notes and look into difficult questions.
    • Do not study on last 2-3 days before the exam. Just revise the formulas and do anything that helps you relax- watch movies, web shows, anything that you like.

    Important Formuals

    Important Formulas

    1. Current - (i) = dq/dt
    2. Drift Velocity- V= (eV/ ml)
    3. Electric Current and Drift Velocity- I= q/t= nAve
    4. Ohm’s Law of Conductors- V=IR
    5. Resistance- R=V/I
    6. Resistivity of a Material- ρ = RA/l
    7. Relation between Resistivity and relaxation time - ρ = m /ne2
    8. Conductivity- σ = 1/ρ
    9. Conductance- 1/R = (1/ρ) (A/l)
    10. Resistance in a series- R = R1+R2+R3

    -V = V1+V2+V3

    - I = I1 = I2 = I3 = Constant

    - V1 = IR1, V2 = IR2, V3 = IR3

    1. Resistance in a parallel- 1/R = 1/ R1 + 1/ R2 +1/ R3

    -I = I1+I2+I3

    - V = V1 = V2 = V3 = Constant

    -I1 = V/R1, I2 = V/R2, I3 = V/R3

    1. Electric Power- P= VI= I2R = V2/R
    2. Unit of Power- 1 watt= 1 volt x 1 amp
    3. Electric Energy- W= Vq = V(It)
    4. Unit of Energy- 1 J= 1 watt sec
    5. Heating Effect of Current- I = I2Rt Joule = I2Rt/J Calorie
    6. Total Power consumed in a parallel combination- P = P1+P2+Pz
    7. Total Power consumed in a series combination- 1/P= 1/P1+1/P2+1/P3

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