15. which one is used to measure electric current?
a) voltmeter
b) ammeter
c) ohmmeter
d) galvanometer
short answer questions
16. define electric charge.
17. state coulomb’s law in words.
18. what is the difference between conductors and insulators?
19. explain how a compass works using magnetic fields.
20. what is the principle of an electric motor?
21. describe how a transformer works.

Question

Accepted Answer

### 15.
# Brief Explanations:
A voltmeter measures voltage, an ohmmeter measures resistance, a galvanometer detects small - scale current or voltage and is often used in experimental set - ups. An ammeter is specifically designed to measure the magnitude of electric current in an electrical circuit.
# Answer:
B. Ammeter

### 16.
# Brief Explanations:
Electric charge is a fundamental property of matter. It can be positive or negative. It is the property that causes matter to experience a force in an electromagnetic field. It is quantized, with the elementary charge $e = 1.6\times10^{- 19}\ C$ being the smallest unit of charge.
# Answer:
Electric charge is a fundamental property of matter that causes it to experience a force in an electromagnetic field, existing as positive or negative and being quantized.

### 17.
# Brief Explanations:
Coulomb's Law states that the magnitude of the electrostatic force between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them. The force is along the line joining the two charges.
# Answer:
The magnitude of the electrostatic force between two point - charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them, and acts along the line joining the charges.

### 18.
# Brief Explanations:
Conductors have a large number of free electrons that can move easily within the material, allowing electric current to flow with relatively low resistance. Insulators have very few free electrons, and thus offer high resistance to the flow of electric current.
# Answer:
Conductors have a large number of free electrons and allow current to flow easily, while insulators have few free electrons and offer high resistance to current flow.

### 19.
# Brief Explanations:
A compass contains a magnetized needle. Earth has a magnetic field. The compass needle aligns itself with Earth's magnetic field lines, with the north - seeking pole of the needle pointing towards Earth's magnetic north pole.
# Answer:
A compass contains a magnetized needle that aligns with Earth's magnetic field lines, with the north - seeking pole pointing towards Earth's magnetic north pole.

### 20.
# Brief Explanations:
The principle of an electric motor is based on the interaction between a magnetic field and a current - carrying conductor. When a current - carrying coil is placed in a magnetic field, a force acts on the coil due to the magnetic field, causing the coil to rotate.
# Answer:
The principle of an electric motor is the interaction between a magnetic field and a current - carrying conductor, where the force on the current - carrying coil in the magnetic field causes it to rotate.

### 21.
# Brief Explanations:
A transformer consists of a primary and a secondary coil wound around a common iron core. An alternating current in the primary coil creates a changing magnetic flux in the core. This changing flux induces an alternating emf in the secondary coil according to Faraday's law of electromagnetic induction. The ratio of the voltages in the primary and secondary coils is related to the ratio of the number of turns in the coils.
# Answer:
A transformer uses Faraday's law of electromagnetic induction. An AC in the primary coil creates a changing magnetic flux in the core, which induces an emf in the secondary coil, and the voltage ratio is related to the turn - ratio of the coils.

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QUESTION IMAGE

Question

Explanation:

15.

Answer:

16.