- Understand the concept of electric fields and their properties.
- Learn how electric forces and fields interact with charged particles.
- Apply mathematical formulas to calculate electric field strength and force.
- Students will be able to define and explain key terms related to electric fields in English.
- Students will be able to discuss the concepts of electric field lines, electric field strength, and electric force using appropriate vocabulary.
- Students will be able to interpret diagrams and solve problems related to electric fields, explaining their reasoning in English.
Let’s familiarize ourselves with the key terms for this topic. Төмендегі кестеде осы тақырып бойынша негізгі терминдер берілген.
English Term | Russian Translation (Перевод на русский) | Kazakh Translation (Қазақша аудармасы) |
---|---|---|
Electric Field | Электрическое поле | Электр өрісі |
Electric Charge | Электрический заряд | Электр заряды |
Electric Force | Электрическая сила | Электр күші |
Field Lines (Electric Field Lines) | Силовые линии (Линии электрического поля) | Күш сызықтары (Электр өрісінің күш сызықтары) |
Point Charge | Точечный заряд | Нүктелік заряд |
Coulomb’s Law | Закон Кулона | Кулон заңы |
Electric Field Strength | Напряженность электрического поля | Электр өрісінің кернеулігі |
Uniform Electric Field | Однородное электрическое поле | Біртекті электр өрісі |
Permittivity of free space (ε0) | Диэлектрическая проницаемость вакуума (ε0) | Бос кеңістіктің диэлектрлік өтімділігі (ε0) |
To help you memorize these terms, you can use flashcards. Check out this set on Quizlet (or create your own!):
Search for Electric Fields Flashcards on Quizlet
Alternatively, create physical flashcards for active recall.
Understand the definitions of key concepts. Төменде негізгі ұғымдардың анықтамалары берілген.
- Electric Field: A region of space around a charged object where an electric force is
- Electric Field Strength (E): The force per unit positive charge at a point in an electric field. It is a vector quantity, measured in Newtons per Coulomb (N C-1) or Volts per meter (V m-1). Formula: E = F/q.
- Coulomb’s Law: States that the
- Electric Field Lines: Imaginary lines used to
- They show the direction of the force on a positive test charge.
- Lines start on positive charges and end on negative charges (or go to infinity).
- The of lines (how close they are) indicates the strength of the field. Closer lines mean a stronger field.
- Field lines never cross.
electric fields. - Uniform Electric Field: An electric field where the field strength is the same at all points in magnitude and direction. Field lines are parallel, equally spaced, and point in the same direction. Often found between two oppositely charged parallel plates.
An electric field is a fundamental concept in physics. It’s a region in space where an electric charge will experience a force. Fields are created by electric charges themselves.
1. Representing Electric Fields: Field Lines
We use electric field lines to visualize electric fields. These lines have specific properties:
- They indicate the direction of the force on a small positive test charge.
- They originate from positive charges and terminate on negative charges (or extend to infinity if there’s an isolated charge).
- The closer the field lines (higher density), the stronger the electric field.
- Field lines never cross each other. If they did, it would imply two different directions of force at the same point, which is impossible.
- Field lines meet conducting surfaces at right angles (90 degrees).
Examples of field patterns:
- Isolated positive charge: Field lines radiate outwards.
- Isolated negative charge: Field lines radiate inwards.
- Two equal opposite charges (dipole): Field lines curve from the positive to the negative charge.
- Two equal positive charges: Field lines repel each other, with a neutral point in between.
- Uniform field (e.g., between parallel charged plates): Field lines are parallel, straight, and equally spaced.
2. Electric Field Strength (E)
Electric field strength at a point is defined as the force (F) per unit positive charge (q) experienced by a small test charge placed at that point.
E = F / q
Units: Newtons per Coulomb (N C-1) or Volts per meter (V m-1). Electric field strength is a vector quantity; it has both magnitude and direction.
The force on a charge q in an electric field E is given by:
F = qE
If q is positive, F is in the same direction as E. If q is negative, F is in the opposite direction to E.
3. Electric Field Strength due to a Point Charge
Using Coulomb’s Law (F = k qQ / r2, where k = 1 / (4πε0)), the electric field strength E at a distance r from a point charge Q can be
:E = F/q = (k qQ / r2) / q
E = kQ / r2 or E = Q / (4πε0r2)
Where:
- Q is the charge creating the field (in Coulombs, C)
- r is the distance from the charge (in meters, m)
- ε0 is the permittivity of free space (8.85 x 10-12 F m-1)
- k is Coulomb’s constant (≈ 8.99 x 109 N m2 C-2)
4. Electric Field Strength in a Uniform Field
In a uniform electric field, such as that between two parallel charged plates, the electric field strength E is also related to the potential difference (V) between the plates and the distance (d) separating them:
E = V / d
This formula is particularly useful for
like capacitors.Check Your Understanding / Өзіңді тексер:
- Easy: What are two key properties of electric field lines?
[/su_spoiler] - Medium: If the electric field strength at a point is 100 N/C, what force would a charge of +3 µC experience at that point?
[/su_spoiler] - Medium: How does the electric field strength change if you double the distance from a point charge?
[/su_spoiler] - Hard (Critical Thinking): Two positive charges, +Q and +4Q, are separated by a distance ‘d’. Is there a point on the line joining them where the electric field is zero? If so, is this point closer to +Q or +4Q? Explain your reasoning without detailed calculation, focusing on the concept of field strength dependence on charge and distance.
[/su_spoiler]
Activity 1: Fill in the Blanks
- The region around a charged object where another charge experiences a force is called an _____________.
- Electric field strength is measured in _________ or _________.
- Electric field lines always start on _________ charges and end on _________ charges.
- Coulomb’s Law describes the _________ between two point charges.
- A field where the strength is the same at all points is called a _________ electric field.
Activity 2: Match the Term with its Definition
Terms: A. Electric Field Lines B. Point Charge C. Electric Field Strength D. Coulomb’s Constant (k) | Definitions: 1. Force per unit positive charge. 2. A constant used in calculating electrostatic force, approximately 8.99 x 109 N m2 C-2. 3. Imaginary lines representing the direction and strength of an electric field. 4. An idealized charge concentrated at a single point in space. |
Watch this video for a visual explanation of electric fields:
This video provides a good introduction to electric fields and field lines.
Problem 1: Calculate the electric field strength at a distance of 3.0 cm from a point charge of +5.0 nC.
[/su_spoiler] [/su_spoiler]Problem 2: A charge of -4.0 µC experiences an electric force of 0.020 N to the right in a uniform electric field. What is the magnitude and direction of the electric field?
[/su_spoiler] [/su_spoiler]Explore electric fields interactively using the PhET «Charges and Fields» simulation.
Simulation Link: Charges and Fields Simulation
You can also embed it using this code (may require your WordPress theme/plugins to support iframes):
<iframe src="https://phet.colorado.edu/sims/html/charges-and-fields/latest/charges-and-fields_en.html" width="100%" height="600" scrolling="no" allowfullscreen></iframe>
Tasks:
- Place a single positive charge (+1 nC) on the screen. Enable «Electric Field» vectors and «Voltage» (equipotential lines). Describe what you observe about the field lines and equipotential lines.
- Add a negative charge (-1 nC) near the positive charge. How does the pattern of field lines change? Where is the field strongest?
- Use the voltage sensor tool. What happens to the voltage value as you move the sensor further away from an isolated positive charge? What about an isolated negative charge?
- Try to create a of charges that produces a region of (nearly) uniform electric field. Describe your setup. (Hint: Think about parallel plates).
Task: Electric Field Experts
In pairs or small groups:
- Choose one of the following electric field configurations:
- Two equal positive charges
- Two equal negative charges
- A positive charge and a negative charge of unequal magnitude (e.g., +2Q and -Q)
- A charged conducting sphere
- Sketch the electric field lines and equipotential lines for your chosen configuration. Clearly label the direction of the field and indicate regions of strong and weak field.
- Prepare a short (2-3 minute) explanation of your diagram to present to another group or the class.
- Challenge: Use a tool like Quizizz or LearningApps.org to create 2-3 multiple-choice questions about your specific field pattern for other students to answer.
Answer the following questions. Show all your working where calculations are required.
- Analysis: An electron (charge -1.6 x 10-19 C, mass 9.11 x 10-31 kg) is accelerated from rest in a uniform electric field of strength 1.2 x 104 N C-1.
a) Calculate the magnitude of the electric force on the electron.
b) Calculate the magnitude of the acceleration of the electron.
c) If the electron travels 5.0 cm in this field, what is its final speed (assuming it starts from rest)?
[/su_spoiler] - Analysis/Synthesis: Two point charges, QA = +2.0 nC and QB = -8.0 nC, are placed 12 cm apart in a vacuum.
a) Determine the point X on the line passing through QA and QB where the net electric field strength is zero. State whether X is between the charges, to the left of QA, or to the right of QB.
b) Sketch the electric field lines for this configuration of charges.
[/su_spoiler] - Synthesis: Describe how you would experimentally determine the direction of the electric field at a point in space. What equipment would you need?
[/su_spoiler] - Application/Analysis: A small sphere of mass 5.0 x 10-4 kg is held stationary in a uniform electric field of 2000 N C-1 directed vertically upwards. What is the charge on the sphere? (Assume g = 9.8 N kg-1).
[/su_spoiler] - Critical Thinking/Evaluation: «Electric field lines are real and physically exist in space because we can see their effects.» Critically evaluate this statement.
[/su_spoiler]
- Save My Exams (A-Level Physics CIE — Electric Fields): Save My Exams — Electric Fields
- PhysicsAndMathsTutor (A-Level CIE — Electric Fields): PhysicsAndMathsTutor — Electric Fields
- Khan Academy (Electric field): Khan Academy — Electric Field Introduction
- CrashCourse Physics (Electric Charge and Electric Fields): CrashCourse Physics #25
Take a few moments to reflect on what you’ve learned:
- What are the three most important concepts you learned about electric fields today?
- Which concept did you find most challenging, and what steps will you take to understand it better?
- How can you relate the concept of electric fields to any real-world phenomena or technologies you know?