Samacheer Class 9 Science - Electric Charge and Electric Current

• (a) presence of electron
• (b) presence of proton
• (c) absence of electron
• (d) absence of proton

Answer:
(c) absence of electron

• (a) creates electric charge
• (b) transfers electric charge
• (c) either (a) or (b)
• (d) neither (a) nor (b)

Answer:
(b) transfers electric charge

Charges are not created; electrons are transferred.

• (a) Joule heating
• (b) Coulomb heating
• (c) Voltage heating
• (d) Ampere heating

Answer:
(a) Joule heating

• (a) electrons
• (b) positive ions only
• (c) both positive and negative ions
• (d) neither (a) nor (b)

Answer:
(c) both positive and negative ions

Current in an electrolyte is due to movement of ions. Electrons do not carry current through the bulk of the electrolyte.

• (a) heating effect
• (b) chemical effect
• (c) flowing effect
• (d) magnetic effect

Answer:
(b) chemical effect

True. An electrically neutral object or system has zero net charge, which means it contains equal amounts of positive and negative charges. In an atom, the number of protons (positive charges) equals the number of electrons (negative charges), making the atom electrically neutral. When an object gains or loses electrons, it becomes charged. Therefore, electrical neutrality is correctly defined as either having zero charge or having equal positive and negative charges that cancel each other out.

False. Correct Statement: An ammeter is connected in series in an electric circuit. An ammeter is a device used to measure electric current flowing through a circuit. It must be connected in series so that the entire current passes through it. If an ammeter were connected in parallel, it would provide an alternate path for current with very low resistance, causing most of the current to bypass the main circuit component and potentially damaging the ammeter. Therefore, ammeters always have very low internal resistance and are always connected in series.

False. Correct Statement: The anode in an electrolyte is positive. In an electrochemical cell or during electrolysis, the anode is the electrode connected to the positive terminal of the power source, making it positively charged. The cathode is the electrode connected to the negative terminal and is negatively charged. At the anode, oxidation occurs where electrons are removed from the substance. At the cathode, reduction occurs where electrons are added. This convention applies in electrolytic cells; in galvanic cells, the anode is negative and the cathode is positive, but in the context of electrolytes during electrolysis, the anode is always positive.

A bird sitting on a single electric wire is safe because it does not complete the circuit. Since the bird is in contact with only one wire, there is no potential difference across its body. Electric current flows only when there is a potential difference and a complete circuit. The bird's feet are at the same potential as the wire it is standing on, so no current flows through its body. However, if the bird simultaneously touches another wire at a different potential or touches the ground while on the wire, it would complete a circuit and current would flow through its body, potentially causing electrocution. This is why birds can safely perch on high power lines without harm.

No. A solar cell does not maintain a constant potential difference across its terminals. The potential difference across a solar cell depends on the intensity of sunlight falling on it and the load connected to it. When sunlight intensity increases, more photons strike the solar cell, generating more electron-hole pairs and increasing the voltage. Conversely, when sunlight intensity decreases, the voltage decreases. Additionally, the voltage also varies with the load connected to the cell because as current is drawn from the cell, the internal resistance causes a voltage drop. Since sunlight intensity changes throughout the day due to cloud cover, time of day, and seasonal variations, the voltage output of a solar cell is not constant but varies continuously.

No, electroplating cannot be done using alternating current. Electroplating requires direct current (DC) to function properly. When alternating current is used, the direction of current flow continuously reverses at regular intervals. This constant reversal means that metal ions do not deposit consistently on the electrode surface. Instead, any metal that has been deposited during one half-cycle gets dissolved back during the next half-cycle when the current direction reverses. As a result, no net accumulation of metal occurs on the electrode, and the electroplating process fails. Therefore, only direct current, which flows in one direction continuously, allows metal ions to move consistently toward the cathode and deposit as a uniform coating.

Answer:
Electrostatic force depends on:

• Magnitude of charges
• Distance between charges
• Nature of medium between them

According to Coulomb’s law:

Electric lines of force are imaginary lines drawn in space around a charged body that represent the direction and strength of the electric field at any point. These lines originate from positive charges and terminate at negative charges. The direction of an electric line of force at any point is the same as the direction of the electric force that would act on a small positive test charge placed at that point. The density of these lines indicates the strength of the electric field in that region. Regions with closely spaced lines have a stronger electric field, while regions with widely spaced lines have a weaker field. Electric lines of force never intersect each other because at any point in space, the electric field can have only one direction.

Electric field is defined as the region around a charged body where another charged particle experiences an electric force. It is a region of influence created by the presence of an electric charge. The electric field exists around every charged object and extends infinitely into space, though its strength decreases with distance from the charge. The strength of the electric field at any point is measured by the force experienced by a unit positive charge placed at that point. Electric fields are produced by stationary charges and can exert forces on other charges placed within the field region. The direction of the electric field at any point is defined as the direction of the force that would act on a positive test charge at that location.

Answer:
Electric current is the rate of flow of electric charge through a conductor.

Where:

• (I) = current
• (Q) = charge
• (t) = time

SI Unit:

Ampere (A)

Answer:
At constant temperature, current flowing through a conductor is directly proportional to the potential difference across it.

Where:

• (V) = voltage
• (I) = current
• (R) = resistance

Answer:

• Electric iron box
• Water heater

Other examples:

• Toaster
• Electric kettle

Answer:

Household appliances are connected in parallel because:

• Each appliance gets same voltage.
• Appliances work independently.
• Failure of one appliance does not affect others.

Answer:

(i) Earthing

Metal body of appliances is connected to ground.

(ii) Trip Switch / Circuit Breaker

Automatically disconnects circuit during overload.

(iii) Fuse

Protects circuit using heating effect of current.

Given:

Comb gets charge:

(a) Which object lost electrons?

• Comb gained electrons.
• Hair lost electrons.

(b) Number of electrons transferred

Charge of one electron:

Using:

Answer:

Given:

Using: