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General physics

    Electric Field Strength and Superposition — Physics Lesson

    🎯 Learning Objectives

    Learning Objectives

    • Calculate the electric field strength at one point due to multiple point charges using the principle of superposition
    • Apply vector addition to determine the resultant electric field
    • Understand the relationship between electric field strength and distance from point charges
    • Analyze complex charge configurations and their electric field patterns
    • Solve problems involving electric field calculations in various geometric arrangements
    🗣️ Language Objectives

    Language Objectives

    • Use precise mathematical language to describe electric field calculations
    • Explain the principle of superposition using appropriate scientific terminology
    • Describe vector addition and components in the context of electric fields
    • Communicate problem-solving strategies for complex charge arrangements clearly
    • Write mathematical expressions and equations for electric field calculations accurately
    📝 Key Terms

    Key Terms

    English TermRussian TranslationKazakh Translation
    Electric Field StrengthНапряженность электрического поляЭлектр өрісінің кернеулігі
    Superposition PrincipleПринцип суперпозицииСуперпозиция принципі
    Point ChargeТочечный зарядНүктелік заряд
    Vector AdditionСложение векторовВекторларды қосу
    Resultant FieldРезультирующее полеНәтижелік өріс
    Coulomb’s LawЗакон КулонаКулон заңы
    Electric Field LinesЛинии электрического поляЭлектр өрісінің сызықтары
    PermittivityДиэлектрическая проницаемостьДиэлектрлік өтімділік
    🃏 Topic Flashcards

    Interactive Flashcards

    Practice with these flashcards to memorize key concepts about electric field strength and superposition.

    📚 Glossary

    Glossary

    Electric Field Strength (E)
    The force per unit positive charge experienced by a small test charge placed in the electric field. Measured in Newtons per Coulomb (N/C) or Volts per meter (V/m).
    Translation
    Russian: Напряженность электрического поля — сила, действующая на единицу положительного заряда, помещенного в электрическое поле. Измеряется в Ньютонах на Кулон (Н/Кл) или Вольтах на метр (В/м).
    Kazakh: Электр өрісінің кернеулігі — электр өрісіне орналастырылған бірлік оң зарядқа әсер ететін күш. Ньютон/Кулон (Н/Кл) немесе Вольт/метр (В/м) өлшенеді.
    Superposition Principle
    The principle stating that the total electric field at any point is the vector sum of the individual electric fields produced by each charge acting independently.
    Translation
    Russian: Принцип суперпозиции — принцип, утверждающий, что общее электрическое поле в любой точке является векторной суммой отдельных электрических полей, создаваемых каждым зарядом независимо.
    Kazakh: Суперпозиция принципі — кез келген нүктедегі жалпы электр өрісі әрбір зарядтың тәуелсіз түрде жасайтын жеке электр өрістерінің векторлық қосындысы болып табылады деген принцип.
    Point Charge
    An idealized charge model where all the charge is concentrated at a single point in space. Used as a simplification for calculations when the size of the charged object is negligible compared to distances involved.
    Translation
    Russian: Точечный заряд — идеализированная модель заряда, где весь заряд сосредоточен в одной точке пространства. Используется как упрощение для расчетов, когда размер заряженного объекта пренебрежимо мал по сравнению с рассматриваемыми расстояниями.
    Kazakh: Нүктелік заряд — барлық заряд кеңістіктің бір нүктесінде шоғырланған зарядтың идеалданған моделі. Зарядталған нысанның өлшемі қарастырылатын қашықтықтармен салыстырғанда ескерілмейтін кезде есептеулер үшін жеңілдету ретінде қолданылады.
    Vector Addition
    The mathematical process of combining two or more vectors to produce a resultant vector. In electric fields, this involves adding the x and y components separately.
    Translation
    Russian: Сложение векторов — математический процесс объединения двух или более векторов для получения результирующего вектора. В электрических полях это включает раздельное сложение x и y компонентов.
    Kazakh: Векторларды қосу — нәтижелік векторды алу үшін екі немесе одан көп векторларды біріктірудің математикалық процесі. Электр өрістерінде бұл x және y компоненттерін бөлек қосуды қамтиды.
    Resultant Electric Field
    The single electric field vector that represents the combined effect of all individual electric fields at a particular point in space.
    Translation
    Russian: Результирующее электрическое поле — единственный вектор электрического поля, который представляет объединенный эффект всех отдельных электрических полей в определенной точке пространства.
    Kazakh: Нәтижелік электр өрісі — кеңістіктің белгілі бір нүктесіндегі барлық жеке электр өрістерінің біріккен әсерін көрсететін жалғыз электр өрісі векторы.
    Coulomb’s Law
    The fundamental law describing the electrostatic force between two point charges: F = kq₁q₂/r², where k is Coulomb’s constant (8.99 × 10⁹ N⋅m²/C²).
    Translation
    Russian: Закон Кулона — фундаментальный закон, описывающий электростатическую силу между двумя точечными зарядами: F = kq₁q₂/r², где k — постоянная Кулона (8.99 × 10⁹ Н⋅м²/Кл²).
    Kazakh: Кулон заңы — екі нүктелік заряд арасындағы электростатикалық күшті сипаттайтын іргелі заң: F = kq₁q₂/r², мұндағы k — Кулон тұрақтысы (8.99 × 10⁹ Н⋅м²/Кл²).
    Electric Field Lines
    Imaginary lines that represent the direction and relative strength of an electric field. They point away from positive charges and toward negative charges.
    Translation
    Russian: Линии электрического поля — воображаемые линии, которые представляют направление и относительную силу электрического поля. Они направлены от положительных зарядов к отрицательным зарядам.
    Kazakh: Электр өрісінің сызықтары — электр өрісінің бағыты мен салыстырмалы күшін көрсететін елестетілген сызықтар. Олар оң зарядтардан теріс зарядтарға қарай бағытталған.
    Permittivity of Free Space (ε₀)
    A fundamental physical constant that appears in Coulomb’s law and other electromagnetic equations. Its value is approximately 8.85 × 10⁻¹² F/m (farads per meter).
    Translation
    Russian: Диэлектрическая проницаемость вакуума — фундаментальная физическая константа, которая появляется в законе Кулона и других электромагнитных уравнениях. Ее значение приблизительно 8.85 × 10⁻¹² Ф/м (фарад на метр).
    Kazakh: Бос кеңістіктің диэлектрлік өтімділігі — Кулон заңында және басқа электромагниттік теңдеулерде пайда болатын іргелі физикалық тұрақты. Оның мәні шамамен 8.85 × 10⁻¹² Ф/м (фарад/метр).
    📖 Theory: Electric Field Strength and Superposition

    Theory: Calculating Electric Field Strength Using Superposition

    Introduction to Electric Field Strength

    The electric field strength at any point in space is defined as the force per unit positive charge that would be experienced by a small test charge placed at that point.

    Kazakh Translation
    Кеңістіктің кез келген нүктесіндегі электр өрісінің кернеулігі сол нүктеге орналастырылған кішкентай сынақ зарядының сезінетін бірлік оң зарядқа келетін күш ретінде анықталады.
    Electric field lines around charges

    Electric field lines showing field direction and strength around positive and negative charges

    Mathematical Definition

    The electric field strength is mathematically defined as:

    E = F/q

    Where:

    • E = Electric field strength (N/C or V/m)
    • F = Force on test charge (N)
    • q = Test charge (C)

    Electric Field Due to a Point Charge

    For a single point charge Q, the electric field strength at distance r is given by:

    E = kQ/r² = Q/(4πε₀r²)

    Where:

    • k = Coulomb’s constant = 8.99 × 10⁹ N⋅m²/C²
    • Q = Source charge (C)
    • r = Distance from charge to point (m)
    • ε₀ = Permittivity of free space = 8.85 × 10⁻¹² F/m
    Kazakh Translation
    Жалғыз нүктелік заряд Q үшін r қашықтықтағы электр өрісінің кернеулігі E = kQ/r² = Q/(4πε₀r²) формуласымен беріледі, мұндағы k — Кулон тұрақтысы, Q — көз заряды, r — зарядтан нүктеге дейінгі қашықтық, ε₀ — бос кеңістіктің диэлектрлік өтімділігі.
    Electric field around single point charge

    Radial electric field around a single positive point charge

    The Principle of Superposition

    When multiple charges are present, the principle of superposition states that the total electric field at any point is the vector sum of the individual fields:

    E⃗total = E⃗1 + E⃗2 + E⃗3 + … = Σ E⃗i

    Kazakh Translation
    Бірнеше заряд болған кезде, суперпозиция принципі бойынша кез келген нүктедегі жалпы электр өрісі жеке өрістердің векторлық қосындысы болып табылады.

    Vector Components and Addition

    When dealing with multiple charges, we must consider the vector nature of electric fields. The process involves:

    StepProcessMathematical Expression
    1Calculate magnitude of each fieldEi = kQi/ri²
    2Determine direction of each fieldθi (angle from x-axis)
    3Calculate x-componentsEx = ΣEicos(θi)
    4Calculate y-componentsEy = ΣEisin(θi)
    5Find resultant magnitudeEtotal = √(Ex² + Ey²)
    6Find resultant directionθ = tan⁻¹(Ey/Ex)
    Vector addition of electric fields

    Vector addition of electric fields from multiple point charges

    Special Cases and Symmetry

    1. Fields Along the Same Line

    When charges are arranged along the same line, electric fields add or subtract algebraically:

    • Same direction: Etotal = E1 + E2
    • Opposite directions: Etotal = |E1 — E2|

    2. Symmetric Arrangements

    For symmetric charge arrangements, some components may cancel out, simplifying calculations.

    Kazakh Translation
    Симметриялы заряд орналасулары үшін кейбір компоненттер жойылып, есептеулерді жеңілдетуі мүмкін.

    Practice Questions

    Question 1 (Easy):

    Calculate the electric field strength at a point 3.0 m away from a +5.0 μC point charge.

    Answer
    Given: Q = +5.0 × 10⁻⁶ C, r = 3.0 m
    Using E = kQ/r²
    E = (8.99 × 10⁹)(5.0 × 10⁻⁶)/(3.0)²
    E = (44.95 × 10³)/9.0
    E = 4.99 × 10³ N/C = 5.0 × 10³ N/C
    Direction: Away from the positive charge

    Question 2 (Medium):

    Two point charges +4.0 μC and -6.0 μC are located 5.0 m apart. Calculate the electric field strength at the midpoint between them.

    Answer
    Given: Q₁ = +4.0 × 10⁻⁶ C, Q₂ = -6.0 × 10⁻⁶ C, distance apart = 5.0 m
    Distance from each charge to midpoint = 2.5 m

    E₁ = kQ₁/r² = (8.99 × 10⁹)(4.0 × 10⁻⁶)/(2.5)² = 5.75 × 10³ N/C (toward Q₂)
    E₂ = kQ₂/r² = (8.99 × 10⁹)(6.0 × 10⁻⁶)/(2.5)² = 8.63 × 10³ N/C (toward Q₂)

    Both fields point in the same direction (toward the negative charge)
    E_total = E₁ + E₂ = 5.75 × 10³ + 8.63 × 10³ = 1.44 × 10⁴ N/C

    Question 3 (Medium):

    Three charges are arranged at the corners of an equilateral triangle with side length 4.0 m. Calculate the electric field at the center if the charges are +2.0 μC, +2.0 μC, and -4.0 μC.

    Answer
    Distance from each corner to center = (4.0/√3) = 2.31 m

    E₁ = E₂ = k(2.0 × 10⁻⁶)/(2.31)² = 3.37 × 10³ N/C
    E₃ = k(4.0 × 10⁻⁶)/(2.31)² = 6.74 × 10³ N/C

    Due to symmetry, the two +2.0 μC charges create fields that partially cancel in the x-direction.
    The y-components from +2.0 μC charges: 2 × 3.37 × 10³ × cos(30°) = 5.84 × 10³ N/C (upward)
    The field from -4.0 μC: 6.74 × 10³ N/C (upward)

    Total field = 5.84 × 10³ + 6.74 × 10³ = 1.26 × 10⁴ N/C (upward)

    Question 4 (Critical Thinking):

    Design a charge configuration using four point charges that creates zero electric field at the center of a square. Explain your reasoning and calculate the required charge magnitudes if the square has side length 2.0 m and two of the charges are +3.0 μC.

    Answer
    Design Strategy:
    For zero field at center, we need symmetry and balance. Since we have two +3.0 μC charges, we need two negative charges to balance them.

    Configuration:
    Place charges at square corners: +3.0 μC, -3.0 μC, +3.0 μC, -3.0 μC in alternating pattern.

    Analysis:
    Distance from corner to center = √2 m
    Each charge creates field: E = k(3.0 × 10⁻⁶)/(√2)² = 1.35 × 10⁴ N/C

    Vector Addition:
    Opposite charges create fields pointing toward/away from center
    Due to symmetry: +3.0 μC charges create components that cancel with -3.0 μC charges
    Net field = 0 N/C

    Alternative Solution:
    Could also use +3.0 μC, +3.0 μC, -3.0 μC, -3.0 μC with appropriate positioning for symmetry.

    🧠 Memorization Exercises

    Exercises on Memorizing Terms

    Exercise 1: Formula Matching

    Electric field formulas

    Match each formula with its correct description:

    Formulas:

    1. E = F/q
    2. E = kQ/r²
    3. Ex = E cos θ
    4. Etotal = √(Ex² + Ey²)

    Descriptions:

    • Resultant magnitude calculation
    • Electric field definition
    • x-component of electric field
    • Field due to point charge

    Answer
    1-B: E = F/q → Electric field definition
    2-D: E = kQ/r² → Field due to point charge
    3-C: Ex = E cos θ → x-component of electric field
    4-A: Etotal = √(Ex² + Ey²) → Resultant magnitude calculation

    Exercise 2: Fill in the Constants

    Physics constants
    1. Coulomb’s constant k = _______ N⋅m²/C²
    2. Permittivity of free space ε₀ = _______ F/m
    3. Relationship: k = 1/(4πε₀) = _______
    4. Electric field units: _______ or _______
    5. The direction of electric field from positive charge is _______

    Answer
    1. 8.99 × 10⁹
    2. 8.85 × 10⁻¹²
    3. 8.99 × 10⁹ N⋅m²/C²
    4. N/C, V/m
    5. radially outward

    Exercise 3: Vector Component Practice

    Vector components diagram

    For an electric field of magnitude 500 N/C at 37° above the horizontal:

    1. x-component = _______ N/C
    2. y-component = _______ N/C
    3. If this field is added to another field of 300 N/C pointing downward, the resultant y-component = _______ N/C
    4. The resultant magnitude would be _______ N/C

    Answer
    1. Ex = 500 cos(37°) = 500 × 0.8 = 400 N/C
    2. Ey = 500 sin(37°) = 500 × 0.6 = 300 N/C
    3. Net Ey = 300 — 300 = 0 N/C
    4. Etotal = √(400² + 0²) = 400 N/C
    🔬 Problem Solving Examples

    Worked Examples

    Example 1: Linear Arrangement of Charges

    Linear charge arrangement

    Problem: Three point charges are arranged in a line: +2.0 μC at x = 0, -4.0 μC at x = 3.0 m, and +1.0 μC at x = 6.0 m. Calculate the electric field at x = 1.5 m.

    🎤 Audio Solution

    Detailed Solution with Pronunciation

    Step 1: Identify distances (pronounced: DIS-tan-ses)

    From +2.0 μC: r₁ = 1.5 — 0 = 1.5 m

    From -4.0 μC: r₂ = 3.0 — 1.5 = 1.5 m

    From +1.0 μC: r₃ = 6.0 — 1.5 = 4.5 m

    Step 2: Calculate field magnitudes

    E₁ = k|Q₁|/r₁² = (8.99×10⁹)(2.0×10⁻⁶)/(1.5)² = 7.99×10³ N/C

    E₂ = k|Q₂|/r₂² = (8.99×10⁹)(4.0×10⁻⁶)/(1.5)² = 1.60×10⁴ N/C

    E₃ = k|Q₃|/r₃² = (8.99×10⁹)(1.0×10⁻⁶)/(4.5)² = 4.44×10² N/C

    Step 3: Determine directions

    E₁: rightward (+x direction) from +2.0 μC

    E₂: rightward (+x direction) toward -4.0 μC

    E₃: rightward (+x direction) from +1.0 μC

    Step 4: Add algebraically (all same direction)

    E_total = E₁ + E₂ + E₃ = 7.99×10³ + 1.60×10⁴ + 4.44×10²

    E_total = 2.44×10⁴ N/C rightward

    📝 Quick Solution

    Brief Solution

    Given: Q₁ = +2.0 μC at x = 0, Q₂ = -4.0 μC at x = 3.0 m, Q₃ = +1.0 μC at x = 6.0 m
    Find: E at x = 1.5 m

    Distances: r₁ = 1.5 m, r₂ = 1.5 m, r₃ = 4.5 m

    Field magnitudes:

    E₁ = 7.99×10³ N/C → (+x)

    E₂ = 1.60×10⁴ N/C → (+x)

    E₃ = 4.44×10² N/C → (+x)

    Result: E = 2.44×10⁴ N/C (+x direction)

    Example 2: Rectangular Charge Configuration

    Rectangular charge arrangement

    Problem: Four charges are placed at the corners of a rectangle: +3.0 μC at (0,0), -2.0 μC at (4.0,0), +1.0 μC at (4.0,3.0), and -1.5 μC at (0,3.0). Find the electric field at the center (2.0,1.5).

    🎤 Audio Solution

    Detailed Solution with Pronunciation

    Step 1: Calculate distances to center

    All distances: r = √[(2.0)² + (1.5)²] = √6.25 = 2.5 m

    Step 2: Calculate field magnitudes

    E₁ = k(3.0×10⁻⁶)/(2.5)² = 4.31×10³ N/C

    E₂ = k(2.0×10⁻⁶)/(2.5)² = 2.88×10³ N/C

    E₃ = k(1.0×10⁻⁶)/(2.5)² = 1.44×10³ N/C

    E₄ = k(1.5×10⁻⁶)/(2.5)² = 2.16×10³ N/C

    Step 3: Find angles and components

    Angle from center to each charge: θ = tan⁻¹(1.5/2.0) = 36.87°

    E₁: θ₁ = 180° + 36.87° = 216.87° (toward charge)

    E₂: θ₂ = 180° — 36.87° = 143.13° (away from charge)

    E₃: θ₃ = 36.87° (away from charge)

    E₄: θ₄ = -36.87° (toward charge)

    Step 4: Calculate components and sum

    Ex = Σ Ei cos θi = -1.73×10³ N/C

    Ey = Σ Ei sin θi = -8.64×10² N/C

    E_total = √(Ex² + Ey²) = 1.93×10³ N/C

    Direction: θ = tan⁻¹(Ey/Ex) = 206.4° from +x axis

    📝 Quick Solution

    Brief Solution

    Setup: Four charges at rectangle corners, find E at center (2.0,1.5)

    All distances to center: r = 2.5 m

    Reference angle: θ = 36.87°

    Field magnitudes:

    E₁ = 4.31×10³ N/C, E₂ = 2.88×10³ N/C

    E₃ = 1.44×10³ N/C, E₄ = 2.16×10³ N/C

    Vector sum:

    Ex = -1.73×10³ N/C

    Ey = -8.64×10² N/C

    E_total = 1.93×10³ N/C at 206.4°

    🔬 Investigation Task

    Interactive Simulation

    Use this PhET simulation to investigate electric field patterns and superposition:

    Investigation Questions:

    1. How does the electric field pattern change when you add more positive charges?
    2. What happens to the field lines when you place equal positive and negative charges close together?
    3. Where are the points of zero electric field in a two-charge system?
    4. How does distance affect the relative strength of fields from multiple charges?
    Brief Answers
    1. Adding more positive charges creates more field lines radiating outward, increasing field strength in most regions
    2. Field lines form dipole pattern — emanating from positive and terminating on negative charge
    3. Zero field points exist on the line connecting two equal opposite charges, closer to the weaker charge
    4. Closer charges dominate the field pattern; distant charges have minimal effect due to 1/r² dependence
    👥 Group/Pair Activity

    Collaborative Learning Activity

    Work with your partner or group to complete this electric field analysis challenge:

    Discussion Points:

    • How does the principle of superposition apply to real-world electric field situations?
    • What strategies help when dealing with complex charge configurations?
    • How do symmetry considerations simplify electric field calculations?
    • What are the practical applications of understanding electric field distributions?

    Group Challenge Activities:

    • Design charge configurations that create uniform electric fields
    • Calculate fields for increasingly complex geometric arrangements
    • Create field line diagrams for various charge combinations
    • Investigate applications in technology (CRT screens, particle accelerators)
    ✏️ Individual Assessment

    Structured Questions — Individual Work

    Question 1 (Analysis):

    A linear quadrupole consists of four charges arranged along the x-axis: +Q at x = -3a, -2Q at x = -a, -2Q at x = +a, and +Q at x = +3a, where Q = 2.0 μC and a = 1.0 m.

    1. Calculate the electric field at the origin (x = 0).
    2. Find the electric field at x = 2a.
    3. Determine the point(s) where the electric field is zero.
    4. Analyze the behavior of the electric field for large distances (x >> a).
    5. Sketch the electric field as a function of position along the x-axis.

    Answer
    a) At origin: E = k[Q/(3a)² — 2Q/a² — 2Q/a² + Q/(3a)²] = k[-4Q/a²] = -7.18×10⁴ N/C
    b) At x = 2a: E = k[Q/(5a)² — 2Q/(3a)² — 2Q/a² + Q/a²] = k[-Q/a²] = -1.80×10⁴ N/C
    c) Zero field occurs at x = ±a√5 ≈ ±2.24a due to symmetry and charge arrangement
    d) For x >> a: E ≈ 0 (quadrupole field falls off as 1/x³, faster than dipole)
    e) Field changes sign at zero points, strongest near ±a positions

    Question 2 (Synthesis):

    Design an electric field configuration using point charges that creates a uniform electric field in a 2.0 m × 2.0 m square region. The field should have magnitude 1000 N/C pointing in the +y direction.

    1. Propose a charge arrangement that could achieve this goal.
    2. Calculate the required charge magnitudes and positions.
    3. Evaluate the uniformity of your solution by calculating the field at multiple points.
    4. Discuss the limitations and practical considerations of your design.
    5. Suggest improvements to increase field uniformity.

    Answer
    a) Use parallel plate approximation with line charges or multiple point charges above and below the region
    b) Place +Q charges in a line at y = +2 m and -Q charges at y = -2 m, with Q ≈ 4.4×10⁻⁸ C per meter
    c) Calculate E at corners and center: variations will be ~10-20% due to finite size effects
    d) Limitations: edge effects, finite charge arrangement, practical charge magnitudes
    e) Use more charges, extend charge distribution further, use conducting plates instead

    Question 3 (Evaluation):

    A proposed particle accelerator design uses electric fields to accelerate charged particles. Analyze a simplified 2D model where particles move through a series of charged rings.

    1. Model each ring as 8 point charges arranged in a circle of radius 0.5 m.
    2. Calculate the axial electric field (along the central axis) for one ring with total charge +1.0 μC.
    3. Design a three-ring system to accelerate electrons from rest to 10% the speed of light.
    4. Evaluate the focusing/defocusing effects on off-axis particles.
    5. Compare your design with realistic accelerator parameters and suggest improvements.

    Answer
    a) Each point charge: q = 1.25×10⁻⁷ C at radius 0.5 m
    b) On axis at distance z: E = 8kq·z/(z² + R²)^(3/2), where R = 0.5 m
    c) For 0.1c: need ~25.6 keV kinetic energy, requires careful spacing and voltage optimization
    d) Radial field components provide focusing for particles slightly off-axis
    e) Real accelerators use continuous electrodes, higher voltages, magnetic focusing elements

    Question 4 (Critical Thinking):

    Lightning rods work by creating strong electric fields that ionize air molecules. Analyze the electric field around a lightning rod during a thunderstorm.

    1. Model the lightning rod as a line charge with linear charge density λ = 10⁻⁶ C/m and height 10 m.
    2. Calculate the electric field at ground level 5 m away from the rod’s base.
    3. Determine the field strength at the rod’s tip if a thundercloud creates a background field of 10⁶ N/C.
    4. Analyze why pointed conductors are more effective than blunt ones for lightning protection.
    5. Evaluate safety distances for people during electrical storms based on field calculations.

    Answer
    a) Line charge model: integrate contributions from each segment of the rod
    b) Field calculation involves integration: E ≈ kλ[h/r√(r² + h²)] ≈ 3.2×10³ N/C
    c) At tip: field enhancement factor ~10-100, so E ≈ 10⁷-10⁸ N/C (breakdown threshold)
    d) Sharp points concentrate field lines, creating higher field strengths for same charge
    e) Safe distance >50 m from tall structures during storms based on step potential and field strength

    Question 5 (Application):

    Electrospray ionization (used in mass spectrometry) relies on strong electric fields to create charged droplets. Design and analyze a simplified electrospray system.

    1. Model the system as a charged needle tip (point charge +Q) facing a grounded plate 2 mm away.
    2. Calculate the required charge Q to achieve 10⁹ N/C field strength at the needle tip.
    3. Analyze the electric field distribution between needle and plate.
    4. Determine the trajectory of a charged droplet (mass 10⁻¹⁵ kg, charge +10e) in this field.
    5. Evaluate the practical limitations and suggest design improvements.

    Answer
    a) Point charge model facing infinite grounded plane (method of images applies)
    b) At tip: E = kQ/r² = 10⁹ N/C, so Q ≈ 1.1×10⁻¹³ C (need tip radius ~1 μm)
    c) Field strongest near tip, decreases toward plate following ~1/r² law with image charge correction
    d) Droplet accelerates toward plate: F = qE, a = qE/m ≈ 10¹⁴ m/s² initially
    e) Limitations: breakdown voltage, space charge effects, droplet size distribution; Improvements: pulsed voltage, coaxial geometry, multiple needles
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