My Solutions to the British Physics Olympiad: BPhO Senior Challenge 2018 Multiple Choice

ZPhysics
21 Feb 202109:37
EducationalLearning
32 Likes 10 Comments

TLDRIn this educational video, the host tackles multiple-choice questions from the 2018 British Physics Olympiad Senior Challenge. Starting with an estimation of a page's thickness, the host explains the process of elimination and the importance of unit consistency in equations. The video covers topics like electrical resistance, dimensional correctness in equations, and the physics of a finger's impact on a beaker's balance. It's an engaging walkthrough aimed at sparking interest in physics problem-solving.

Takeaways
  • 📝 The video discusses multiple choice questions from the 2018 British Physics Olympiad Senior Challenge.
  • 🔍 The first question is an estimation problem about the thickness of a page, suggesting it's about 0.1 millimeters.
  • ⚡ The second question explains the unit of electrical resistance in terms of base units, deriving it from the formula for voltage.
  • 🔋 A volt is defined as a joule per coulomb, and the video breaks down the units of a joule into kg m²/s².
  • ⚖️ The third question is about choosing the correct formula for the speed of an astronomical object, emphasizing the importance of dimensional correctness.
  • 🌌 The fourth question is an estimation of the number of atoms in a grain of sand, with the correct answer being approximately 10^20 atoms.
  • 🧠 A useful fact mentioned is that the number of electrons in the human body is about 10^28.
  • 💧 The final question involves a physics concept where a student's finger in water causes an increase in the balance reading due to Newton's third law.
  • 📚 The video aims to be helpful for those preparing for the British Physics Olympiad and encourages viewers to subscribe for more content.
  • 🤓 The presenter uses clear examples and explanations to help viewers understand the concepts behind the physics questions.
Q & A

  • What is the main topic of the video?

    -The main topic of the video is to discuss and solve multiple choice questions from the British Physics Olympiad Senior Challenge from 2018.

  • Why can't the thickness of a page in an exam paper be one millimeter?

    -The thickness of a page can't be one millimeter because it would be easily measurable with a ruler, and a page is typically about a tenth of a millimeter in thickness.

  • What is the unit of electrical resistance in terms of base units?

    -The unit of electrical resistance, the ohm, in terms of base units is equivalent to a joule per coulomb.

  • What is the formula for energy that the video uses to explain the unit of a joule?

    -The video uses the formula E = 1/2 mv^2 to explain the unit of a joule, which is kg m^2/s^2.

  • What is the unit of charge, and why is it an ampere-second?

    -The unit of charge is the coulomb, which is an ampere-second because charge (Q) is equal to current (I) times time (t), so Q = It.

  • How does the video explain the dimensional correctness of an equation?

    -The video explains that for an equation to be dimensionally correct, the units on the left must match the units on the right. It uses the example of calculating the speed of an astronomical object.

  • Why is option D the correct choice for the speed of an astronomical object problem?

    -Option D is correct because it is the only option that results in units of meters per second, which is the unit for speed, by canceling out the kilograms and leaving the units of c^2/(at).

  • What is the approximate number of atoms in a typical coarse grain of sand found on a beach?

    -The approximate number of atoms in a grain of sand is 10^20.

  • How does the video relate the number of atoms in a grain of sand to the human body?

    -The video states that the number of electrons in a human body is about 10^28, which is a much larger number than the number of atoms in a grain of sand.

  • What happens to the reading on a top pan balance when a student sticks his finger in the water?

    -The reading on the balance will increase due to the up thrust acting on the student's finger, as explained by Newton's third law.

Outlines
00:00
📚 Estimation and Units in Physics Problems

The first paragraph introduces a video on solving the British Physics Olympiad Senior Challenge from 2018. It begins with an estimation question about the thickness of a page, suggesting it's about 0.1 millimeters. The presenter then explains the unit of electrical resistance, Ohm, in terms of base units, deriving it from the formula for voltage and current, and relating it to the Joule, the unit of energy. The summary also touches on the correct approach to a problem involving the speed of an astronomical object, emphasizing the importance of dimensional analysis in equations.

05:02
🔍 Dimensional Analysis and Estimation in Physics

The second paragraph continues the discussion on physics problem-solving with a focus on dimensional analysis. It discusses the incorrectness of certain answers to a question about the speed of an astronomical object due to incorrect units. The presenter explains why answer D is correct by showing how the units cancel out to result in meters per second, which is the unit for speed. The paragraph also includes an estimation of the number of atoms in a grain of sand, suggesting it's approximately 10^20, and touches on the concept of Newton's third law in the context of a balance with a beaker of water and a student's finger, explaining how the balance reading would increase due to the upward thrust of the water.

Mindmap
Keywords
💡British Physics Olympiad Senior Challenge
The British Physics Olympiad Senior Challenge is a prestigious competition designed to test the knowledge and problem-solving skills of advanced high school students in physics. In the video, it serves as the context for the discussion of multiple-choice questions, indicating the high level of difficulty and the need for deep understanding of physics concepts.
💡Estimation
Estimation refers to the process of approximating a value or quantity. In the context of the video, it is used to guess the thickness of a page, highlighting the importance of making educated guesses based on everyday experience and understanding of physical dimensions.
💡Millimeter
A millimeter is a unit of length in the metric system, equal to one-thousandth of a meter. The video uses the millimeter to discuss the thickness of a page, emphasizing the need for an accurate understanding of measurement units in physics.
💡Volt
The volt is the derived unit for electric potential, electric potential difference, and electromotive force. In the script, it is defined as a joule per coulomb, showing the relationship between energy, charge, and voltage, which is fundamental to understanding electrical circuits and phenomena.
💡Joule
The joule is the SI unit of energy, work, or amount of heat. In the video, it is related to the formula for kinetic energy (E = 1/2 mv^2), illustrating how the joule is used to quantify energy transfer in various physical processes.
💡Coulomb
The coulomb is the SI unit of electric charge. It is used in the video to explain the unit of electrical resistance (ohm) and to show how charge relates to current and time, which is essential for understanding electricity and magnetism.
💡Dimensional Analysis
Dimensional analysis is a problem-solving technique used to convert one unit to another and to check the consistency of units in equations. The video emphasizes its importance in physics, especially when determining the correct formula for calculating the speed of an astronomical object.
💡Equation
An equation is a mathematical statement that asserts the equality of two expressions. In the context of the video, equations are used to describe physical laws and to solve problems, such as finding the speed of an object or the number of atoms in a grain of sand.
💡Newton's Third Law
Newton's Third Law states that for every action, there is an equal and opposite reaction. The video uses this law to explain the effect on a balance when a finger is inserted into water, demonstrating the mutual forces between objects.
💡Balance
A balance is a device used to measure the mass of an object by comparing it with known masses. In the video, a top pan balance is used to illustrate Newton's Third Law, showing how the interaction between the water and the finger affects the balance's reading.
💡Astronomical Object
An astronomical object refers to any entity outside Earth's atmosphere, such as stars, planets, and moons. The video mentions calculating the speed of an astronomical object, which involves complex physics and the application of dimensional analysis to ensure the units are consistent.
💡Units
Units are used to express the magnitude of a physical quantity. The video script discusses the importance of units in ensuring equations are dimensionally correct, such as when calculating the speed of an astronomical object or the number of atoms in a grain of sand.
Highlights

Introduction to the British Physics Olympiad Senior Challenge from 2018.

Estimation of the thickness of a page in an exam paper, suggesting it's about a tenth of a millimeter.

Explanation of why the thickness of a page cannot be one millimeter or 10 millimeters.

Discussion on the unit of electrical resistance, Ohm, in terms of base units.

Derivation of the unit of a volt as joule per coulomb.

Conversion of joule into base units using the formula for kinetic energy.

Explanation of the unit of coulomb as an ampere second.

Solving a problem involving the speed of an astronomical object with dimensional analysis.

Dimensional correctness of equations and how it applies to the problem at hand.

Elimination of incorrect answers based on unit mismatch in the equation.

Selection of the correct answer using dimensional analysis for the speed of an astronomical object.

Estimation of the number of atoms in a grain of sand, suggesting it's approximately 10^20.

Comparison of the number of atoms in a grain of sand to the number of electrons in the human body.

Discussion on the effect of a student's finger on the balance when placed in a beaker of water.

Explanation of Newton's third law in the context of the balance and the water's reaction to the finger.

Illustration of how the balance reading increases due to the interaction between the water and the finger.

Conclusion and invitation to subscribe for more solutions to the British Physics Olympiad.

Transcripts

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Physics OlympiadMultiple ChoiceUnit ConversionEducational ContentEstimation SkillsElectrical ResistanceEnergy FormulaAstronomical SpeedNewton's Third LawBalance ReadingScience Tutorial