Physics-17 Electromagnetic forces Prequiz

When gripping a wire, so that thumb points in the convectional current direction. the fingers show the direction of the magnetic field lines is called the ________.

• Right hand grip rule

• armature

• motor effect

• Fleming's left hand rule

• commutator

Answer explanation

We can remember this diagram using the right-hand rule. If you point your pointer finger in the direction the positive charge is moving, and then your middle finger in the direction of the magnetic field, your thumb points in the direction of the magnetic force pushing on the moving charge.

The rotating part of an electrical generator is called a(n) _______.

• Right hand grip rule

• armature

• motor effect

• Fleming's left hand rule

• commutator

Answer explanation

An armature is the rotating coil or coils of a dynamo or electric motor.

When a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field and this is called the ________.

• Right hand grip rule

• armature

• motor effect

• Fleming's left hand rule

• commutator

Answer explanation

The Motor effect is when a wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles. This is called the motor effect. There is a force at right angles to the current and the magnetic field.

The _______ is a rule that gives the direction of the force on a current-carrying wire in a magnetic field according to the directions of the current and the field

• Right hand grip rule

• armature

• motor effect

• Fleming's left hand rule

• commutator

Answer explanation

Fleming's left-hand rule for electric motors is one of a pair of visual mnemonics, the other being Fleming's right-hand rule, for generators. They were originated by John Ambrose Fleming, in the late 19th century, as a simple way of working out the direction of motion in an electric motor, or the direction of electric current in an electric generator.

When current flows through a conducting wire, and an external magnetic field is applied across that flow, the conducting wire experiences a force perpendicular both to that field and to the direction of the current flow (i.e they are mutually perpendicular). A left hand can be held, as shown in the illustration, so as to represent three mutually orthogonal axes on the thumb, fore finger and middle finger. Each finger is then assigned to a quantity (mechanical force, magnetic field and electric current). The right and left hand are used for generators and motors respectively.

The _____ is a device that controls the direction of the flow of current through an electric motor

• Right hand grip rule

• armature

• motor effect

• Fleming's left hand rule

• commutator

Answer explanation

Th commutator is an attachment, connected to the armature of a motor or generator, through which electrical connection is made and which ensures that the current flows as direct current.

A diagram that uses circles to display elements of different sets. Overlapping circles show common elements is called a(n) _____.

• Venn diagram

• plotting compass

• solenoid

• field lines

• vacuum tube

Answer explanation

A Venn diagram is an illustration that uses circles to show the relationships among things or finite groups of things. Circles that overlap have a commonality while circles that do not overlap do not share those traits. Venn diagrams help to visually represent the similarities and differences between two concepts.

A small ______ is used for finding the direction of a magnetic field.

• Venn diagram

• plotting compass

• solenoid

• field lines

• vacuum tube

Answer explanation

The shape and direction of a magnetic field may be investigated using plotting compasses. A plotting compass is like a small bar magnet, with a north and south pole. The arrow of the plotting compass represents the north pole.

A _____ is a coil of wire with an electric current in it

• Venn diagram

• plotting compass

• solenoid

• field lines

• vacuum tube

Answer explanation

A solenoid is a cylindrical coil of wire acting as a magnet when carrying electric current.

Lines coming from an object representing the strength of the force. The denser the lines, the stronger the force are _______.

• Venn diagram

• plotting compass

• solenoid

• field lines

• vacuum tube

Answer explanation

An electric field line is an imaginary line or curve drawn through a region of empty space so that its tangent at any point is in the direction of the electric field vector at that point. The relative closeness of the lines at some place gives an idea about the intensity of electric field at that point.

A(n) ______ is a sealed glass tube from which most of the air has been evacuated

• Venn diagram

• plotting compass

• solenoid

• field lines

• vacuum tube

Answer explanation

A vacuum tube, also called a valve in British English, is an electronic device used in many older model radios, television sets, and amplifiers to control electric current flow. The cathode is heated, as in a light bulb, so it will emit electrons.