ST23102 Science 6 Past Paper PDF

## ST23102: Science 6 English Program, Samsenwitthayalai ### 1. Electricity Electricity is a form of energy that is transformed from another energy form and can transform into another forms of energy. #### 1.1 Electric Current When the source of electricity is connected with an electric device...

## ST23102: Science 6 English Program, Samsenwitthayalai ### 1. Electricity Electricity is a form of energy that is transformed from another energy form and can transform into another forms of energy. #### 1.1 Electric Current When the source of electricity is connected with an electric device with a conduction wire and if the circuit is closed, the current is flowing through the circuit. **Electric Current:** Electric current is the amount of electric charge passing through a cross-sectional area of a wire in one second. *** **Practice 1** 1. Electric charge 3x10⁵ coulombs pass through a conduction wire in 2.5 seconds. Determine the current flow in the wire. 2. A current of 25 mA flows through a wire for 5 minutes. What is the amount of charge passing through the cross-sectional area of the wire? 3. A current of 0.8 A flows through a wire for 4 minutes. How many electrons are passing through the cross-sectional area of the wire? (Given: one electron contains 1.6x10^-19 Coulombs) 4. If the current flows through a wire as shown in the figure below, what is the amount of charge flowing through the wire from 0 to 10 seconds. *** #### 1.2 Types of Electric Current * **Direct Current (DC):** Is a current flowing in one direction. * **Alternative Current (AC):** Is a current flowing in two directions. #### 1.3 Measuring of Electric Current - Instrument used: **Ammeter** - Ammeter must be connected **in series with any point** - A good ammeter must have **very low resistance.** #### 2. Relationship between potential difference (V), current (I) and resistance (R) ##### 2.1 Resistance (R) Resistance is the property of an object that resists the current flow in the circuit. **Unit of resistance:** Ohm (Ω) * High resistance --> **Low current flow** * Low resistance --> **High current flow** ##### 2.2 Potential difference (V) The potential difference between two points is the energy losses from electric charge 1 coulomb when passes two points. **Unit of potential difference:** Volt (V) ##### 2.3 Measuring the potential difference: - The potential difference is the difference between two points. - A measuring device called **Volt meter** must be connected **in parallel between two points**. - Voltmeter must have **very high (∞) resistance.** #### 2.4 Ohm's Law **Ohm's Law experiment** **Result** | Voltage (V) | Current (I) (A) | Resistance (Ω ) | |---|---|---| | 1.5 | 0.1 | 15 | | 3.0 | 0.2 | 15 | | 4.5 | 0.3 | 15 | | 6.0 | 0.4 | 15 | **Ohm's law states that "the current through a conductor between two points is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and is inversely proportional to the resistance between them.** *** **Practice 2** 1. Current 35 mA flows through a light bulb which resistance is 6 ohm. Determine potential difference across the light bulb. 2. An electric device with resistance 44 ohm is connected with a potential difference of 220 V Determine current flows through the electric device. 3. A copper wire with resistance of 25 ohm is connected with a potential difference 50 V. Determine the current flows through the copper wire. *** #### 4. A flash light bulb used with 1.5 V battery and current 300 mA (a) Determine resistance of the light bulb. (b) If we use until voltage reduces to 1.2 V, determine current flows through the light bulb. #### 5. A resistance wire is connected with potential difference 4.0x10³ V and the current flow 1.0 mA. If this resistance is connected to a potential difference 1.2 V, how much does current flow through this resistance? #### 6. From the following, a resistance is 50 ohm and the current is flow 200 mA. How much voltmeter reading? #### 7. From the following, if the voltmeter is reading as 20 volts and the resistance is 50 ohm, how much the current flows? #### 8. From the following, if ammeter is read as 50 mA and voltmeter is read as 10 V, how much is the resistance? #### 4. Resistance of a conduction wire (R) ##### 4.1 Factor on the resistance of conduction wire * **Type of conduction wire:** - The metal arranged from the best conductance **Ag, Cu** -> **the lower resistant** - The more cross-sectional area -> **the higher resistant** * **Cross sectional area of the conduction wire:** - The more cross-sectional area -> **the lower resistant** - The less cross-sectional area -> **the higher resistant** * **The length of the conduction wire:** - The longer the wire -> **the higher resistant** - The shorter the wire -> **the lower resistant** ##### 4.2 Formula for resistance $R = \frac{ρl}{A}$ $R$: resistant of a conduction wire (Ω) $ρ$: resistivity of the metal (Ωm) $l$: length of a conduction wire (m) $A$: cross-sectional area (m²) ##### 4.3 Relationship between two different resistance **Case 1:** **Case 2: With stretching** *** **Practice 3** 1. The relationship between potential difference and current through a nichrome wire is shown in the figure below. If the ratio of length and cross-sectional area is 2x10⁵ m^-1, determine the resistivity of the wire. 2. A metal wire with cross-sectional area of 0.05 cm² and 2.5 m long has the resistivity 8x10^-8 Ωm. If the current flows through the wire 40 mA, determine the potential difference across the wire. *** #### 9. Metal A and B are the same metal. Metal A cross-sectional area is 3 times of metal B and the length of metal A is 4 times of metal B. If metal B resistance is 6 ohm, what is the resistance of metal A? #### 10. Metal x and y are the same. The ratio of length for x:y is 2:3 and the ratio of radius for x:y is 2:1. Determine resistance of metal x when resistance of y is 12 ohm. #### 11. A metal wire X has the resistance two times of metal Y and the length of wire X is half of metal Y. If the cross-sectional area of wire X is twice of Y, determine the ratio of resistivity of wire X to Y. #### 12. Metal A and B are different. The resistivity of A:B is 4:5 and the length of A:B is 5:2 and the diameter of A:B is 2:1. Determine the ratio of resistance for A:B. #### 13. The potential difference between two ends of a conduction wire is 5.25 V and the current is measured as 0.15 A. Determine the length of this wire if its resistance is 0.25 ohm when its length is 2 m. #### 14. If the length and cross-sectional area of wire A is half of those of wire B, what is the resistance of wire A comparing to resistance of wire B?