Solution:

Fill in the blanks

• (a) Most liquids that conduct electricity are solutions of acids, bases and salts.
• (b) The passage of an electric current through a solution causes chemical effects.
• (c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.
• (d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

Solution:

Explanation for Deflection of Magnetic Needle in a Tester

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection due to the presence of an electric current. If the solution is conductive, it allows the flow of electric current when a potential difference is applied across the tester's terminals. This electric current creates a magnetic field around the tester’s wires. According to Ampere's Circuital Law, a current-carrying conductor produces a magnetic field, which interacts with the magnetic needle of the tester, causing it to deflect.

The degree of deflection depends on the strength of the electric current, which in turn depends on the concentration and conductivity of the solution. The more conductive the solution, the greater the flow of current, leading to a stronger magnetic field and a greater deflection of the needle.

Solution:

Name three liquids, which when tested in the manner shown in Fig.11.9, may cause the magnetic needle to deflect:

• Mercury
• Salt water
• Iron filings suspended in a liquid

Solution:

The bulb does not glow in the setup shown in Fig.11.10. List the possible reasons. Explain your answer.

There could be several possible reasons why the bulb does not glow in the setup shown in Fig.11.10:

1. Broken Bulb: The filament inside the bulb may be broken, causing an open circuit. Without the filament being intact, the electric current cannot flow through the bulb, and it will not glow.
2. Loose Connections: The wires or connections in the circuit may be loose or not properly connected. If the circuit is incomplete, the current will not flow, and the bulb will remain off.
3. Power Supply Issue: There may be no power supply or the battery may be dead. Without a proper voltage source, the current cannot flow through the circuit, and the bulb will not light up.
4. Burnt Fuse: If there is a fuse in the circuit and it has burnt out, the flow of electricity will be interrupted, preventing the bulb from glowing.
5. Defective Bulb: The bulb itself may be defective, even if the filament appears intact. Sometimes manufacturing defects can prevent the bulb from lighting up.
6. Incorrect Connection in the Circuit: If the circuit is connected incorrectly, such as if the polarity of the battery is reversed, the bulb may not glow because the current is unable to flow in the correct direction.

Solution:

5. A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that :

• (i) liquid A is a better conductor than liquid B. CORRECT
• (ii) liquid B is a better conductor than liquid A.
• (iii) both liquids are equally conducting.
• (iv) conducting properties of liquid cannot be compared in this manner.

Solution:

Does Pure Water Conduct Electricity? If Not, What Can We Do to Make It Conducting?

Pure water does not conduct electricity because it lacks free ions that are necessary for the flow of electric current. In pure water, the concentration of ions is very low. For water to conduct electricity, it must contain dissolved substances that dissociate into ions. These ions are the charge carriers that allow the current to pass through the water.

To make water conduct electricity, we can add substances like salt (sodium chloride, NaCl), acid (like hydrochloric acid, HCl), or base (like sodium hydroxide, NaOH). These substances dissociate in water to produce positive and negative ions, which facilitate the conduction of electricity.

Solution:

Why the Main Electrical Supply is Shut Off Before Using Water Hoses in Case of a Fire

In case of a fire, firemen shut off the main electrical supply for the area before using water hoses to prevent the risk of electrical shocks. Water is a good conductor of electricity, and if it comes into contact with live electrical wires, it can conduct electricity, posing a danger to the firemen and others in the vicinity. By shutting off the electrical supply, the risk of electrocution is minimized, ensuring the safety of everyone involved in fighting the fire.

Solution:

A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

The compass needle deflects more in the case of seawater because seawater contains dissolved salts and minerals, which can increase its electrical conductivity. These dissolved ions, such as sodium and chloride, make seawater a better conductor of electricity compared to drinking water. The tester likely works by detecting the presence of electrical currents or magnetic fields, which are influenced by the conductivity of the water. Since seawater is a better conductor, the tester detects stronger magnetic fields, causing the compass needle to deflect more.

Solution:

Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

No, it is not safe for the electrician to carry out electrical repairs outdoors during a heavy downpour. Water is a good conductor of electricity, and when it rains heavily, the risk of electrical shocks increases significantly. If the electrician comes into contact with electrical circuits or equipment while standing on wet ground or working in the rain, the electrical current can pass through the body, leading to serious injury or even death.

Moreover, electrical equipment may malfunction when exposed to water, causing short circuits and fire hazards. It is important for electricians to ensure that the area is dry and that all electrical repairs are carried out with proper safety measures, including the use of insulated tools and protective equipment, to prevent accidents during adverse weather conditions like heavy rain.

Solution:

What could be the reasons for deflection of compass needle in rainwater?

Paheli found that the compass needle showed deflection when she tested the rainwater. There could be several reasons for this:

• The rainwater might contain dissolved salts and minerals, which could make it slightly conductive. This conductivity can create a magnetic field that interacts with the compass needle.
• Rainwater might have picked up impurities from the atmosphere, such as dust, pollutants, or ions, which could also affect its electrical properties.
• Even though rainwater is often considered pure, it may still contain small amounts of dissolved substances that can influence the magnetic field.

Solution:

Objects That Are Electroplated

• Jewelry (e.g., gold-plated rings, necklaces)
• Cutlery (e.g., silver-plated spoons, forks)
• Car parts (e.g., chrome-plated bumpers)
• Electrical connectors (e.g., gold-plated circuit boards)
• Coins (e.g., gold or silver-plated commemorative coins)
• Bathroom fittings (e.g., chrome-plated taps, showerheads)
• Musical instruments (e.g., brass instruments with silver or gold plating)
• Home appliances (e.g., electroplated handles on refrigerators)
• Watches (e.g., gold-plated watch bands)
• Optical instruments (e.g., silver-plated telescope lenses)

Solution:

Answer:

In the process of purifying copper, the thick rod of impure copper is used as the anode, and the thin plate of pure copper is used as the cathode. The anode should be attached to the positive terminal of the battery because, during electrolysis, oxidation occurs at the anode. At the anode, copper from the impure copper rod dissolves into the solution as copper ions ($Cu^{2+}$), while at the cathode, copper ions from the solution gain electrons and get deposited as pure copper. Therefore, the anode is connected to the positive terminal to facilitate the oxidation of copper and its transfer to the cathode.