# 10 Common Errors Students Make While Solving Physics Problems

- Nov 23, 2016
- Sudipto Das

Physics problems can be one of the main causes of a headache for many students. Most of them might have grabbed the concept well, know it by heart, but as soon as numericals crop up, they tend to struggle with the same. There are a few common standout mistakes that students make while engaging with physics problems. In this article, we have compiled a list of 10 common errors that students make while solving physics problems. Let’s go through them without further ado.

**Mixing units**

This one is the most common of all errors. It’s a silly mistake on one hand, troublesome on the other.

Students should always take into account the units provided in the problem. They should do their calculations in a consistent system of units. They can either follow the MKS system or the CGS system as per requirement, but they should keep in mind that they convert each and every unit into one specific system to do their calculations.

For example,

If a problem contains certain units in meter and hour-

- They have to convert hour into seconds to do the calculation in a MKS system and find the result. Keep the meter as it is because it tallies with the MKS system of units.

Or

- They have to convert meter into centimeter and hour into seconds to do the calculation in a CGS system and find the result.

Keeping a consistent system of units is the key. Use either MKS or CGS but DO NOT mix up.

**Expressing in the wrong units **

This is basically dependent on the question. Say, for example, the problem asks for an answer in the MKS system and you failed to notice that. You left the answer in the CGS system of units. That’s technically an error from the point of view of the question and you’ll be getting zero marks for all that hard work. So it’s always advisable to read the question in detail.

**Confusing radians and degrees **

Most physics problems use degrees but not all. Take, for example, angular velocity and acceleration. That is exactly when you’ve to ensure the fact that you are using radians in a calculation. Keep that in mind even when using your calculators.

**Mixing up Sines and Cosines**

Physics students often mix up sines and cosines. Make sure that you know these relationships by heart.

sin θ = opposite/hypotenuse= b/a.

cos θ = adjacent/hypotenuse= c/a.

tan θ = opposite/adjacent = b/c.

**Errors in vector recognitions**

Say for example, while adding vectors, vector addition technique needs to be implemented. That means determining vectors in 2 components. Many students have the habit of summing up the vector magnitudes without realizing the fact that they should add components instead.

**Ignoring latent heat **

When you are given a physics problem that involves a phase change, like from ice to water, you mustn’t forget to take latent heat into account. If you fail to consider the latent heat in your answer, you’ll come to the wrong answer.

**Mistaking refraction angles**

While dealing with problems that are based on refraction, do make sure that you get the angles right. The angles are measured with respect to the “perpendicular” (AKA “normal”) to the interface from one medium to another. Many students incorrectly take into account the angle between the ray of light and the interface between the 2 mediums.

**Mistaking signs in Kirchoff loops**

Kirchoff’s laws are mainly used to find the currents in a circuit. Many students run into trouble with problems that are based on Kirchoff’s laws because they make simple errors with the signs. The trick is to get the signs right and you’ll easily get the correct result in no time.

*Tip*-

To get the signs right, you should put in arrows to mark the direction of all currents.

**Incorrect addition of Resistors**

Students make common mistakes in calculating resistance in series and parallel circuits.

When two resistors (R1 and R2) are in series,

R= R1 + R2.

When 2 resistors are in parallel, total resistance would be something like-

1/R= 1/R1 + 1/R2.

**Using wrong directional rays in ray diagrams**

Ray diagrams are an integral part of a significant physics topic-light. Students make common mistakes in ray direction by using wrong-directional rays.

There are many other stand-out errors associated with physics. But the ones mentioned above are the most common of all. With that, we’ll bring this article to an end. Hope you had a good read.

### Sudipto Das

Sudipto writes technical and educational content periodically for wizert.com and backs it up with extensive research and relevant examples. He's an avid reader and a tech enthusiast at the same time with a little bit of “Arsenal Football Club” thrown in as well. He's got a B.Tech in Electronics and Instrumentation.

Follow him on twitter @SudiptoDas1993

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