Magnetism And Electromagnetism Book Back Questions 9th Science Lesson 5

9th Science Lesson 5

5] Magnetism And Electromagnetism

Book Back Questions with Answer and Do You Know Box Content

Do You Know?

Some sea turtles (loggerhead sea turtle) return to their birth beach many decades after they were born, to nest and lay eggs. In a research, it is suggested that the turtles can perceive variations in magnetic parameters of Earth such as magnetic field intensity and remember them. This memory is what helps them in returning to their homeland.

Problem 1: A conductor of length 50 cm carrying a current of 5 A is placed perpendicular to a magnetic field of induction 2 x 10^-3 T. Find the force on the conductor.

Solution: Force on the conductor = ILB = 5 x 50 x 10^-2 x 2 x 10^-3 = 5 x 10^-3 N

Problem 2: A current carrying conductor of certain length, kept perpendicular to the magnetic field experiences a force F. What will be the force if the current is increased four times, length is halved and magnetic field is triples?

Solution: F = I L B = (4I) x (L/2) x (3 B) = 6 F. Therefore, the force increases six times.

Michael Faraday (22^nd Sep, 1791 – 25^th Aug, 1867) was a British Scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism and electrolysis.

A step up transformer increases the voltage but it decreases the current and vice versa. Basically there will be loss of energy in a transformer in the form of heat, sound etc.

Problem 3: The primary coil of a transformer has 800 turns and the secondary coil has 8 turns. It is connected to a 220 V ac supply. What will be the output voltage?

Solution: In a transformer, E_S / E_P = N_S/N_P

E_S = N_S/N_P x E_P = 8/800 x 220 = 220/100 = 2.2 volt.

Choose the best answers:

1. Which of the following converts electrical energy into mechanical energy?

(a) Motor

(b) Battery

(c) Generator

(d) Switch

2. Transformer works on

(a) AC only

(b) DC only

(c) Both AC and DC

3. The part of the AC generator that passes the current from the armature coil to the external circuit is

(a) Field magnet

(b) Split rings

(c) Slip rings

(d) Brushes

4. The unit of magnetic flux density is

(a) Weber

(b) Weber/meter

(c) Weber/meter²

(d) Weber.meter²

Fill in the blanks:

1. The SI unit of magnetic field induction is ________________.

2. Devices which is used to convert high alternating current to low alternating current is _____________.

3. An electrical motor converts ______________.

4. A device for producing electric current is _______________.

Match the following:

1. Magnetic material – Oersted

2. Non-magnetic material – Iron

3. Current and magnetism – Induction

4. Electromagnetic induction – Wood

5. Electric generator – Faraday

State true or false. If false, correct the statement:

1. A generator converts mechanical energy into electrical energy.

2. Magnetic field lines always repel each other and do not intersect.

3. Fleming’s Left hand rule is also known as Dynamo rule.

4. The speed of rotation of an electric motor can be increased by decreasing the area if the coil.

5. A transformer can step up direct current.

6. In a step down transformer the number of turns in primary coil is greater than that of the number of turns in the secondary coil.

Answers:

Choose the best answers:

1. Motor 2. AC only 3. Brushes 4. Weber/meter²

Fill in the blanks:

1. Tesla 2. Step down transformer 3. Electrical energy into Mechanical energy 4. Generator

Match the following:

1.Magnetic material- Iron

2.Non-magnetic material – Wood

3.Current and magnetism- Oersted

4.Electromagnetic induction- Faraday

5.Electric generator- Induction

State true or false. If false, correct the statement:

1.True

2.True

3.True

4.False

Correct answer: The speed of rotation of an electric motor can be increased by increasing the area of the coil

5.False

Correct answer: A transformer can step up alternating current

6.True