Among the following physical quantities, which one is a scalar quantity (that is, it has magnitude only and no direction)?

Introduction / Context:
This question tests a fundamental concept in physics: the difference between scalar and vector quantities. Scalars are described completely by magnitude alone, while vectors need both magnitude and direction for full description. In mechanics and electromagnetism, many commonly used quantities fall clearly into one of these two categories. Being able to classify typical quantities correctly is essential for solving problems and understanding how physical laws are expressed in vector form.

Given Data / Assumptions:

• The options are electric current, electric field, acceleration and linear momentum.
• Vector quantities require direction as well as magnitude.
• Scalar quantities do not have an inherent direction in space.
• We must identify which quantity is treated as scalar in standard physics.

Concept / Approach:
Acceleration and linear momentum are clearly vector quantities in mechanics. Acceleration describes rate of change of velocity and points in the direction of the change. Linear momentum equals mass times velocity and therefore has the same direction as velocity. Electric field at a point in space also has both magnitude and direction, indicating the force per unit positive charge at that point, and is thus a vector field. Electric current, although it involves charges moving in a certain direction, is defined in terms of the rate of flow of charge through a cross section and is treated as a scalar quantity in basic circuit theory. Current has magnitude and a sign (for conventional direction), but it is not represented as a vector in three dimensional space in elementary physics.

Step-by-Step Solution:
Step 1: Consider acceleration. It changes with direction when an object turns, even at constant speed, so it must be a vector quantity. Step 2: Consider linear momentum, defined as p = m * v, where v is velocity. Because velocity is a vector, momentum is also a vector. Step 3: Examine electric field, which is defined as force per unit charge. The direction of the field indicates the direction of the force on a positive test charge, so it is clearly a vector. Step 4: Examine electric current, which in elementary circuit theory is described by a magnitude (for example, 2 ampere) and a sign that indicates conventional direction but is not usually handled as a vector in space. Step 5: Conclude that among the listed options, electric current is treated as a scalar quantity.

Verification / Alternative check:
A practical check is to think about how these quantities are written in formulas and problem statements. Acceleration, momentum and electric field are often shown with arrows over them in textbooks and used with vector addition rules. Electric current, on the other hand, is typically written without vector notation and combined algebraically as a scalar when applying Kirchhoff laws in circuit analysis. This difference in notation and use supports the classification of electric current as scalar in standard introductory physics.

Why Other Options Are Wrong:
Electric field is a vector quantity because it has a specific direction at each point and is represented as a vector field. Acceleration is a vector because it indicates not just how fast velocity changes but also in which direction the change occurs. Linear momentum is a vector since it depends on velocity, which itself is directional.

Common Pitfalls:
Some students get confused because electric current flows in a particular direction in a wire and think it must therefore be a vector. However, in basic physics and engineering, current is treated as a scalar magnitude with a chosen reference direction, not as a full vector in three dimensional space. Understanding this distinction helps avoid mistakes in vector related questions and clarifies why certain quantities appear in vector equations while others do not.

Final Answer:
Among the given options, the quantity that is treated as a scalar is Electric current.