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Understanding IB Physics command terms is vital for success in the course, as these terms guide you on how to approach and answer exam questions effectively. In this blog post, we will break down these command terms, so that you can develop the skills necessary to excel in IB Physics.
IB Physics Command Terms
Define – Give the precise meaning of a word, phrase, concept or physical quantity. For example, if you were asked to define 'velocity,' you would state that it is the rate of change of displacement with respect to time, including both magnitude and direction.
Draw – Represent by means of a labelled, accurate diagram or graph, using a pencil. A ruler (straight edge) should be used for straight lines. Diagrams should be drawn to scale. Graphs should have points correctly plotted (if appropriate) and joined in a straight line or smooth curve. For example, if you were asked to draw a free-body diagram for an object in equilibrium, you would accurately represent the object with arrows showing all the forces acting on it, ensuring each force is labelled, with the length of the arrows proportional to the magnitude of the forces.
Label – Add labels to a diagram. For instance, if you were asked to label the parts of a wave diagram, you would clearly identify and mark key features such as the displacement, time, amplitude, trough, period, and wavelength.
List – Give a sequence of brief answers with no explanation. For example, if you were asked to list the fundamental SI units, you would state: meter, kilogram, second, ampere, kelvin, and mole.
Measure – Obtain a value for a quantity. For example, if you were asked to measure the acceleration due to gravity using a pendulum, you would record the length of the pendulum and the time for a number of oscillations to calculate the value of g.
State – Give a specific name, value or other brief answer without explanation or calculation. For example, if you were asked to state Newton's second law of motion, you would simply write that force equals mass times acceleration.
Write down – Obtain the answer(s), usually by extracting information. Little or no calculation is required. Working does not need to be shown. For example, if you were asked to write down the wavelength of a light wave given in a problem, you would directly state the value provided in the question, such as "500 nm."
Annotate – Add brief notes to a diagram or graph. For example, if you were given a graph of a wave showing a wave, you would label the key features such as the wavelength, amplitude, etc., and also include brief notes explaining these features.
Apply – Use an idea, equation, principle, theory or law in relation to a given problem or issue. For example, if asked to apply Newton's second law of motion to determine the acceleration of a car, you would use the formula F = ma, where F is the force applied to the car and m is its mass. By rearranging the formula to a = F/m, you would then substitute the given values for force and mass to calculate the car's acceleration.
Calculate – Obtain a numerical answer showing the relevant stages in the working. For instance, If you were asked to calculate the density of an object that has a mass of 50kg and a volume of 10m3 you would substitute these values into the formula density = mass/volume and obtain the final answer: 50kg/10m3 =5kg/m3.
Describe – Give a detailed account. For example, if you were asked to describe the photoelectric effect, you would explain how light striking a metal surface causes the emission of electrons from that surface. You would detail the key concepts: photons of light have energy that can be transferred to electrons, and if the energy is above a certain threshold, it can free the electrons from the metal. Additionally, you would describe how the number of emitted electrons depends on the intensity of the light and how the kinetic energy of the electrons depends on the frequency of the incident light, with the results supporting the quantum theory of light.
Distinguish – Make clear the differences between two or more concepts or items. For example, if you were asked to distinguish between scalar and vector quantities, you would explain that scalar quantities have only magnitude and no direction, while vector quantities have both magnitude and direction, you would highlight that vectors are represented with arrows showing direction and length proportional to magnitude, whereas scalars are represented by numerical values alone. In this type of question you would focus only on the differences between the two (or more) concepts.
Estimate – Obtain an approximate value. For instance, if you were asked to estimate the speed of a car traveling that has traveled 100km in 1.5 hours, you would use the formula for average speed, which is speed = distance/time: 100km/1.5 hours = ~ 67km/h.
Formulate – Express precisely and systematically the relevant concept(s) or argument(s). For example, if you were asked to formulate the principle of conservation of momentum, you would express it as follows: "In a closed system, the total momentum before and after an event remains constant, provided no external forces act on it. For instance, in a collision between two objects, the total momentum of the system before the collision is equal to the total momentum after the collision, assuming no external forces are involved.
Identify – Provide an answer from a number of possibilities. For example, if you were asked to identify the type of interaction between two charged particles, you would identify it as an electromagnetic interaction.
Outline – Give a brief account or summary. For example, if you were asked to outline the basic principles of Ohm's Law, you would summarize that it states the relationship between voltage, current, and resistance in an electrical circuit. Specifically, it asserts that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.
Plot – Mark the position of points on a diagram. For example, if you were asked to plot a distance-time graph for an object's motion, you would mark the position of data points on the graph where the x-axis represents time and the y-axis represents distance. You would then plot each measured distance corresponding to its time value, accurately positioning each point according to the data provided.
Analyse – Break down in order to bring out the essential elements or structure. For example, if you were asked to analyse the relationship between the frequency and wavelength of electromagnetic waves, you would start by breaking down the fundamental formula You would examine how changes in wavelength affect frequency and vice versa, illustrating that as wavelength increases, frequency decreases proportionally, and vice versa. You might include a discussion of how this relationship applies to different types of electromagnetic waves, such as radio waves and gamma rays, highlighting the essential structure of the formula and its implications for understanding wave behavior.
Comment – Give a judgment based on a given statement or result of a calculation. For example, if you were asked to comment on the result of a calculation showing that the gravitational force between two objects is 9.8 N, you would evaluate the significance of this result. You might discuss whether the calculated force is consistent with expected values based on the objects' masses and the distance between them. Additionally, you could consider any possible sources of error in the measurement or calculation process and how these might affect the reliability of the result.
Compare – Give an account of the similarities between two (or more) items or situations, referring to both (all) of them throughout. For example, if you were asked to compare the behavior of two types of waves – transverse waves and longitudinal waves – you would focus on their similarities: both types of waves transfer energy through a medium, and both can be characterized by properties such as wavelength, frequency, and speed. You would also discuss how both types of waves follow the wave equation
Compare and contrast – Give an account of similarities and differences between two (or more) items or situations, referring to both (all) of them throughout. For this type of question, you would also focus on the differences (transverse waves oscillate perpendicular to the direction of propagation, while longitudinal waves oscillate parallel to it; transverse waves can travel through solids but not through fluids, whereas longitudinal waves can travel through both solids and fluids, etc.).
Construct – Display information in a diagrammatic or logical form. For example, if you were asked to construct a diagram of the electric field around a charged sphere, you would draw a diagram showing the sphere at the center, with arrows representing the direction of the electric field lines radiating outward from the sphere. You would label the sphere, the electric field lines, and any relevant distances or charges.
Deduce – Reach a conclusion from the information given. For example, if you are given that a light wave passes from air into water and you know the angle of incidence and the refractive indices of both media, you can deduce the angle of refraction in the water. For instance, if the angle of incidence is and the refractive index of water is 1.33, you would use Snell's Law to determine that the angle of refraction is approximately
Demonstrate – Make clear by reasoning or evidence, illustrating with examples or practical application. For example, if you were asked to demonstrate the concept of Newton's First Law of Motion, you would illustrate it by showing how an object remains at rest or in uniform motion unless acted upon by an external force. You could use a practical example, such as a book lying on a table that remains stationary until you push it, or a car that continues to move at a constant speed until the driver applies the brakes.
Derive – Manipulate a mathematical relationship to give a new equation or relationship. For example, if you were asked to derive the formula for gravitational potential energy, you would start with the general relationship for work done, . By substituting the gravitational force and the distance as height , you would manipulate the equation to derive , which represents the gravitational potential energy.
Design – Produce a plan, simulation or model. For instance, if you were asked to design an experiment to investigate the factors affecting the period of a simple pendulum, you would need to produce a plan that includes varying the length of the pendulum, keeping other factors like mass and amplitude constant, and measuring the time taken for multiple oscillations. The experiment should also include a method to record and analyze the data, ensuring the results are accurate and reliable.
Determine – Obtain the only possible answer. For example, if you were asked to determine the speed of an object using the formula , you would simply divide the given distance by the given time to obtain the only possible value for the speed .
Discuss – Offer a considered and balanced review that includes a range of arguments, factors or hypotheses. Opinions or conclusions should be presented clearly and supported by appropriate evidence. For example, if you were asked to discuss the impact of increasing the angle of a projectile on its range, you would start by reviewing the theoretical principles involved, such as the relationship between angle and range in projectile motion and discuss factors such as air resistance and initial velocity, supporting your discussion with relevant evidence.
Evaluate – Make an appraisal by weighing up the strengths and limitations. For example, if you were asked to evaluate the use of a pendulum to measure gravitational acceleration, you would assess the strengths, such as its simplicity and accuracy when using precise measurements. You would also consider limitations, like the sensitivity to air resistance and the need for accurate timing devices.
Explain – Give a detailed account including reasons or causes. For example, if you were asked to explain why an object in free fall accelerates at a constant rate, you would detail that this acceleration is due to the force of gravity acting on the object. You would describe how, in the absence of other forces like air resistance, the gravitational force causes the object to increase its velocity uniformly.
Hence – Use the preceding work to obtain the required result. For example, if you were given a problem where you have already calculated the velocity of an object and now need to find its kinetic energy, you would use the velocity value obtained in the previous calculations to determine the kinetic energy by substituting the previously found velocity into the kinetic energy formula.
Hence or otherwise – It is suggested that the preceding work is used, but other methods could also receive credit. For example, if you are asked to determine the acceleration of an object and you have already calculated its final velocity and time, you might use the a = v - u/t based on the previous work. However, you could also use another method, such as analyzing a force diagram or applying Newton’s second law if relevant information is provided.
Justify – Give valid reasons or evidence to support an answer or conclusion. For example, if you are asked to justify the choice of using a particular type of sensor for measuring temperature in an experiment, you would need to provide reasons such as the sensor’s accuracy, range, sensitivity, and response time. You might compare it to other sensors available, explaining why it is more suitable for the experiment's requirements based on the data sheets or performance specifications.
Predict – Give an expected result. For example, if you are asked to predict the outcome of increasing the voltage across a resistor in a circuit, you would use Ohm’s Law to determine the expected change in current. Based on the relationship , you would predict that as the voltage increases, the current through the resistor will also increase proportionally, assuming the resistance remains constant.
Show – Give the steps in a calculation or derivation. For example, if asked to show that the kinetic energy of a moving object is given by , where is the mass and is the velocity, you would start with the basic principles of work and energy. Using the definition of kinetic energy as the work done to accelerate the object, you would substitute the relevant values into the equation to confirm that simplifies to 1/2
Show that – Obtain the required result (possibly using information given) without the formality of proof. “Show that” questions do not generally require the use of a calculator. For example, if asked to show how to calculate the density of an object, you would use the formula: density = mass/volume to calculate the density of a given object.
Sketch – Represent by means of a diagram or graph (labelled as appropriate). The sketch should give a general idea of the required shape or relationship, and should include relevant features. For example, if asked to sketch a wave on a graph, you would draw a smooth, sinusoidal curve that represents the wave’s oscillation over time. Label the axes as time and displacement, and mark the wave’s amplitude, wavelength, and frequency.
Solve – Obtain the answer(s) using algebraic and/or numerical and/or graphical methods. For example, if asked to solve for the final velocity of an object in free fall using the formula , where is the initial velocity, is the acceleration due to gravity, and is the time, you would substitute the given values into the formula.
Suggest – Propose a solution, hypothesis or other possible answer. For example, if asked to suggest a method to reduce energy loss in an electrical circuit, you might propose using insulation materials to reduce heat dissipation.
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