2 marksShort AnswerSection A

(a) (i) Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it. (ii) An alpha particle while passing through a magnetic field gets projected towards north. In which direction will an electron project when it passes through the same magnetic field ? OR (b) (i) What is a solenoid ? (ii) Draw the pattern of magnetic field lines of the magnetic field produced by a solenoid through which a steady current flows.

Magnetic Effects of Electric Current

Force on a Current-Carrying Conductor and Solenoid

Official Answer

Option (a)

(i) Name and Statement of the Rule:

Name: Fleming's Left-Hand Rule.
State: Stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other. If the first finger (forefinger) points in the direction of the magnetic field and the second finger (middle finger) points in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

(ii) Direction of Electron Projection:

An $\alpha$ -particle is a positively charged particle. Its direction of motion represents the direction of the electric current. Since it gets projected towards the North, the magnetic force acting on it is directed towards the North.
An electron is a negatively charged particle. When it passes through the same magnetic field in the same direction as the $\alpha$ -particle, the equivalent current direction for the electron is opposite to its motion (and opposite to that of the $\alpha$ -particle).
Since the charge of an electron is opposite to that of an $\alpha$ -particle, the magnetic force experienced by the electron will be in the exact opposite direction. Therefore, the electron will project towards the South.

OR

Option (b)

(i) Solenoid:

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

(ii) Pattern of Magnetic Field Lines around a Solenoid:

The magnetic field lines inside a current-carrying solenoid are parallel straight lines, indicating a uniform magnetic field. Externally, the field lines emerge from the North pole and merge at the South pole, forming continuous closed loops similar to a bar magnet.

Magnetic Field Lines of a Solenoid

Fleming's left-hand rulemutually perpendicularforefingermiddle fingerthumbalpha particleelectronSouthsolenoidinsulated copper wirecylinder

Marking Scheme

10.5 marks
20.5 marks
31 mark
41 mark
51 mark

Hint

Recall Fleming's Left-Hand Rule where the thumb represents force, the forefinger represents the magnetic field, and the middle finger represents the current. For charged particles, positive charge motion represents current, while negative charge motion is opposite to current.

Quick Oral Answer

Fleming's Left-Hand Rule is used to find the direction of force on a current-carrying conductor in a magnetic field. The thumb points to the force, the index finger to the magnetic field, and the middle finger to the current.

Analysis & Explanation

For part (a)(ii), the magnetic force $\vec{F}$ on a moving charge $q$ with velocity $\vec{v}$ in a magnetic field $\vec{B}$ is given by $\vec{F} = q(\vec{v} \times \vec{B})$ . Since the charge of an electron is negative ( $q_e = -e$ ) and the charge of an alpha particle is positive ( $q_{\alpha} = +2e$ ), entering the same magnetic field with the same velocity results in forces in opposite directions. Thus, if the alpha particle is deflected North, the electron must be deflected South.

Common Mistakes

1Confusing Fleming's Left-Hand Rule with the Right-Hand Thumb Rule.
2Forgetting that the direction of current is opposite to the direction of motion of electrons.
3Drawing open magnetic field lines for a solenoid instead of closed continuous loops.

Interesting Facts

The magnetic field pattern of a current-carrying solenoid is almost identical to that of a bar magnet, and it can be used to create strong temporary magnets called electromagnets.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 2 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Magnetic Effects of Electric Current" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Force on a Current-Carrying Conductor and Solenoid" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2022 paper.