cbse class 8 electric current
Grade 8, Science- Chemistry
Embark on a fascinating journey into the realm of the chemical effects of electric current in this lesson.
- Define Electrical Energy:
- ⚡ Electricity = Electrical Energy
- 🌿 Pollution-free & efficient
- Conductors vs. Insulators:
- Conductors: Allow electricity ⚡ (e.g., metals, graphite)
- Insulators: Resist electricity (e.g., rubber, plastic)
- Components of Electric Tester:
- 🔋 Electric cell
- 💡 Torch bulb
- 📏 Connecting copper wires
- Troubleshooting Electric Tester:
- 🔗 Loose connections? Tighten.
- 💡 Fused bulb? Replace.
- 🔄 Used-up cell? Replace.
- How Does a Bulb Glow?
- 💡 Glows due to electric current
- 🌡️ Heating effect causes filament to glow
- Alternatives to Electric Bulbs:
- 💡 LED (Light Emitting Diode)
- 🧭 Magnetic compass
- LED Definition:
- 💡 Light Emitting Diode
- 💡 Glows with weak current
- 🌈 Used in various applications
- Uses of LED:
- 💡 Less energy consumption
- ⏳ Longer functional life
- 💸 Expensive, can replace CFL
- Magnetic Compass:
- 🧭 Detects weak current
- 🧲 Based on magnetic effect
- 🔄 Needle deflection indicates current
- Electrical Conductivity:
- ⚡ Measure of current-carrying ability
- ⚡ Conductors have high conductivity
- ⚡ Insulators have low conductivity
- Liquids as Conductors/Insulators:
- Good Conductors: Lemon juice, tap water, vinegar
- Bad Conductors: Alcohol, petrol, kerosene
- What are Ions?
- ⚛️ Charged atoms
- 🤝 Cations (positive) & Anions (negative)
- Difference Cations vs. Anions:
- Cations: Positive charge
- Anions: Negative charge
- Electrolytes:
- ⚗️ Compounds ionize in solution
- ⚡ Conduct electricity (e.g., salt in water)
- Non-Electrolytes:
- 🚱 Do not conduct electricity (e.g., glucose)
- Define Electrolysis:
- ⚡ Decomposition of electrolyte with electric current
- Electrodes:
- ⚙️ Metal rods for current entry/exit
- Difference Cathode vs. Anode:
- Cathode: Connected to negative terminal
- Anode: Connected to positive terminal
- Voltameter:
- ⚡ Electrolytic cell
- 🛢️ Contains electrodes and electrolyte
- Effects of Electric Current:
- 🌡️ Heating, 🧲 Magnetic, ⚗️ Chemical
- Chemical Effect of Electric Current:
- 🔄 Electrolysis
- ⚗️ Chemical reactions during current flow
- Chemical Effects Examples:
- 🗜️ Bubbles, 🌈 Color change, ⚙️ Metal deposits
- Chemical Effect Explanation:
- 🌊 Acidified water + Current = O₂ & H₂
- Uses of Electrolysis:
- 🏭 Metal extraction, 💨 Gas production, 🔩 Electroplating
- Electroplating Process:
- 🛢️ Copper sulfate solution
- 💡 Current → Copper deposition
- ⚙️ Anode dissolves, cathode gains copper
- Uses of Electroplating:
- 💍 Jewelry, 🚗 Car parts, 🚿 Taps, 🍴 Utensils
1. Define Electrical energy?
- Electricity provides us a form of energy called Electrical energy
- It is pollution free and most efficient energy
2. Difference between Conductors and Insulators?
| Conductors | Insulators |
| Materials that allow electricity to flow through them easily are called as Conductors | Materials that do not allow electricity to flow through them easily are called as insulators |
| Ex: All metals, Graphite is a non metal but it is a conductor | Ex: rubber, plastic, wood etc |
To test whether a particular material is a conductor or insulator we are using electric tester
3. What are the components of Electric tester??
An Electric tester consists of
- Electric cell
- Torch bulb fitted in a holder
- Some connecting copper wires
4. What are the possible reason that an electric tester is not working??
Connections may be lose – Make sure that all the connections are tight
Bulb is fused – Replace the fused bulb with the new one.
Cell is used up – Replace the drained cell with the new cell.
5. How does a bulb glow??
- The bulb glows when the electric current passes through the electrical tester due to the heating effect of the current
- When current passes through the bulb the filament of the bulb gets heated due to high temperature and starts to glow
6. What are the other alternatives used in the place of electric bulb ??
- LED Light Emitting Diode
- Magnetic compass
7. Define LED??
- LED means Light Emitting Diode
- LED glows even when weak current passes through it
- LEDs are coloured lights in retail stores, stages, bridges and keypad of mobile phones
The two wires (leads) are attached to LED
When connecting to circuit
- Longer lead is connected to the positive terminal of the battery
- The shorter lead is connected to the negative terminal of the battery
8. Uses of LED?
- LED consume less energy
- They function for longer time
- But they are expensive
- LED’s can be replaced with CFL
9. What is a Magnetic Compass??
- Magnetic compass is a device that can detect weak current flowing through wire
- It is based on magnetic effect of electric current
- Deflection of the needle of magnetic compass shows that electric current is flowing through the wire
10. What is Electrical conductivity??
- Electrical conductivity is a measure of ability of the substance to carry the electric current
- Conductors have high electrical conductivity
- Insulators have low electrical conductivity
11. List few liquids as a good and bad conductors of electricity ??
Good conductors
- Lemon juice
- Tap water
- Vinegar
- Dilute HCl
- Dilute KOH
Bad conductors
- Alcohol
- Petrol
- Kerosene
- Oil
- Mustard oil
12. What are ions??
- When an atom loses or gains an electron it forms ions.
- Electrically charged atom or group of atoms are called ions
- That are two ions. Cations and anions
13. Difference between cations and anions??
| Cations | Anions |
| Positively charged ions are called Cations | Negatively charged ions are called Anions |
| When an atom loses electron it becomes positively charged ion | When an atom gains electron it becomes negatively charged ions |
14. What are Electrolytes??
- Chemical compounds whose molecules ionise into positively and negatively charged ions in a solution are called Electrolytes
- Electrolytes are chemical compounds that conduct electricity when dissolved in water
- Ex: When sodium chloride (salt) is dissolved in water it produces sodium ions (Na+)and chloride ions (Cl-)
15. What are Non Electrolytes??
- Non electrolytes are chemical compounds that do not conduct electricity when dissolved in water
- Example glucose and alcohol dissolve in water but do not form ions so they do not conduct electricity
16. Define Electrolysis??
- Decomposition of the electrolyte when electric current is passed through it is called Electrolysis
- Ex: When electric current is passed through aqueous solution of sodium chloride yet decomposes into sodium cations and chlorine anions. This is called Electrolysis.
17. What are Electrodes??
Metal rods or plates through which electric current enters or leaves the electrolyte is called Electrodes.
18. Difference between Cathode and Anode?
| Cathode | Anode |
| Electrode connected to negative terminal of the cell is called Cathode | Electrode connected to positive terminal of the cell is called Anode |
| During electrolysis the positively charged ions present in the electrolyte most towards the Cathode | During electrolysis the negatively charged ions move towards and Anode |
19. What is Voltameter??
- Voltameter is also called as Electrolytic cell
- Glass or plastic container containing to electrodes and electrolyte is called voltameter
- It converts electrical energy into chemical energy
- In voltameter the process of electrolysis is carried out
20. What are the effects of Electric current??
- Heating effect
- Magnetic effect
- Chemical effect
21. What is the Chemical effect of electric current?
- When electric current is passed through an electrolyte chemical reactions takes place.
- This is the chemical effect of electric current
22. What are some chemical effects of electric current??
- Bubbles of a gas may be formed on the electrodes
- Deposits of metal may be seen on electrodes.
- Change of colour may occur in the solution
23. Explanation for a chemical effect:
When current is passed through acidified water
- H+ ions move towards the negatively charged terminal of the battery
- OH – ion move towards positively charged terminal of the battery
- OH – ions lose electrons to get neutralized and form Oxygen gas
24. What are the various uses of Electrolysis?
- Extraction of the metals from their ores.
- When an electric current is passed through molten sodium chloride the sodium Na+ deposited at the cathode and the chlorine gases evolved at the anode
- Aluminium and potassium are extracted from their ores by electrolysis
- Electrolysis is used for the manufacture of chemicals such as Oxygen gas chlorine gas hydrogen gas
- Electrolytic refining (purification) of metals by electrolysis. Ex: Metals Copper, Zinc, Tin, Silver and Gold
- Electroplating: Method of coating a metal surface with a thin layer of superior metal with the help of electric current is called Electroplating
25. Describe the process of Electroplating?
- Copper sulphate is dissolved in water it forms copper ions and sulphate ions.
- When current is passed through the solution the copper ions move towards the cathode and sulphate ions move towards the anode
- At cathode the copper ions gains electron supplied by the electric current and forms copper atoms and thy deposit on the surface of the iron strip
- Sulphate ions do not take part in the chemical reaction
- Copper atom in the copper plate loses electrons to form copper ions that goes into copper sulphate solution
- So anode loses copper atoms to copper ions
- Cathode gains equal number of copper ions to form copper atoms
- Therefore anode slowly dissolves into solution while layer of copper get deposited on the cathode
26. What are the uses of Electroplating?
- Metals used for making jewellery like gold or silver are very expensive
- Artificial jewelleries are electroplated with copper to make them look like gold
- Iron objects are electroplated with chromium nickel or zinc to protect them from rusting.
- Chromium plating is done in many objects such as car parts water taps kitchen utensils gas burners bicycle handlebar wheel rims etc.
Check out the other chapter notes
Physics
Chemistry
Chemical Effects of Electric Current
Biology
