Magnetism and the motor effect：練習問題

A student investigates the magnetic field around a long straight wire. They use a plotting compass to map the field lines when a large direct current flows through the wire.

Which of the following correctly describes the shape and direction of the magnetic field lines in a plane perpendicular to the wire?

A straight wire of length \( 0.80\text{ m} \) carries a current of \( 5.0\text{ A} \). It is placed at right angles to a uniform magnetic field with a magnetic flux density of \( 0.15\text{ T} \). A force is exerted on the wire. If the current is doubled and the length of the wire in the field is halved, what is the new force acting on the wire?

A conductor of length \( 25\text{ cm} \) is placed in a uniform magnetic field with a flux density of \( 0.40\text{ T} \). The wire is at right angles to the field lines. When a current of \( 2.0\text{ A} \) flows through the wire, what is the magnitude of the magnetic force acting on it?

A rigid square coil consisting of \( 10 \) turns, each with a side length of \( 0.05\text{ m} \), is placed in a uniform magnetic field. The plane of the coil is perpendicular to the field. If the magnetic flux density is \( 0.80\text{ T} \) and a current of \( 3.0\text{ A} \) flows through the wire, calculate the total force acting on one side of the coil.

A straight wire of length \(0.25\text{ m}\) carries a current of \(2.0\text{ A}\). It is placed at right angles to a uniform magnetic field with a flux density of \(0.40\text{ T}\). Calculate the magnetic force exerted on the wire and state the rule used to determine its direction.

A student investigates the magnetic force acting on a copper rod placed in a uniform magnetic field. The rod has a length of 0.05 m and is connected to a DC power supply. The magnetic flux density of the field is 0.08 T.