### Combination Of Resistances Class 10th Science Lab Manual CBSE Solution

##### Question 1.What is zero error?Answer:If the pointer of the meter does not coincide with zero of the scale, this type of error in reading of the scale is called a Zero error.Question 2.What is least count?Answer:The smallest value that can be measured accurately by an instrument is called its least count.Question 3.Suppose the ammeter you are using in this experiment does not have positive and negative markings , How will you use such ammeter?Answer:We will connect the ammeter or Voltmeter arbitrary in the circuit and observe the deflection of the pointer. If the deflection occurs in the opposite direction then by interchanging the terminal connection, we can use these devices.Question 4.Suppose the deflection go beyond the full scale. What will you infer from such observation?Answer:If the deflection on ammeter goes beyond the full scale , we infer that:1. The higher range ammeter has to be used to measure higher current.2. The applied voltage is very high thus will require a high range voltmeter to measure applied voltageQuestion 5.Why it is advised to clean the ends of connecting wires before connecting them?Answer:It is advised to clean the ends of connecting wires to remove the insulating layer if any from to ends of the wire. Also, to remove any dust from the ends of the wire to ensure better flow of electrons in the junction.Question 6.While taking the reading the student observe that pointer on voltmeter is 15th division when voltmeter least count is 0.05V. Find the observed reading of voltmeter?Answer:Observed reading = Least count × Number of division= 0.05 × 15= 0.75 VQuestion 7.In a series combination, what happens to voltage and current?Answer:In series combination:1. Current flowing across a different resistor connected in series are same2. Voltage in a series is the sum of the voltage across the different resistor.Question 8.What is the equivalent resistance for a series combination & parallel combination?Answer:The equivalent resistance Req=R1+R2+…….+Rn.The equivalent resistance in a parallel connection is given as: Question 9.In parallel combination, is the current same or voltage same in the circuit?Answer:In parallel combination:1. The voltage across the resistor remains the same.2. The current across the combination is the sum of the current across the different resistor.Question 10.Why are the standard resistances made up of manganin wire?Answer:The standard resistance coils are made up of manganin wire. The reasons are:i. The variation of resistance with a rise in temperature is very less as compared to other metal.ii. The resistivity of the material is very high & any resistance value can be made from it. Therefore, it is used as standard resistance.Question 11.What should be characteristics of standard resistance?Answer:1. The value of resistance should not change with time.2. The value of resistance should almost remain the same with a change in temperature.3. It should be convenient sizes.Question 12.Why connecting wires are made of copper?Answer:The connecting wires are made of copper because copper has low resistivity and it conducts the current without offering much resistance.Question 13.How many times will be the equivalent resistance of two identical resistors be increased if the parallel arrangement is changed to a series arrangement?Answer:The effective resistance in parallel combination is That of series combination is Rs = 2R. Thus, we get Rs = 4Rp, i.e., equivalent resistance increases four times.Question 14.Can you distinguish between resistor and resistance?Answer:The resistor is a device which offers resistance, whereas resistance is the property of the resistor.Question 15.In what way household appliances should be connected?Answer:The household appliances should be connected in parallel in order to get equal voltage for each appliance and ensure that if one is a switch “on” or ”off,” others working are not affected.Question 16.Draw a diagram which shows the direction of current & the current carriers.Answer:The direction of current is from the positive terminal of the battery, it goes on through the components & then enters through negative terminal.The current carriers are electrons and the motion of electrons is opposite from the electric current. Question 17.Why is ammeter always connected in series in a circuit?Answer:Ammeter is always connected in series with circuit as it should offer low resistance to the components added in the series. In this ways, the current can be measured accurately in low resistance.Question 18.Why is voltmeter always connected in parallel?Answer:Voltmeter should be connected in parallel because in parallel connection, the potential difference is same. Question 19.Which device has high resistance voltmeter or ammeter?Answer:Voltmeter has very high resistance and ammeter has negligible resistance. This is because when voltmeter is connected in parallel across any two points, it will draw very less current (due to high resistance), hence it can measure the voltage accurately.Question 20.Why closed path is required for flow of current?Answer:The closed path is necessary for electrons to move in a particular direction.Question 21.What happens to the resistance of a conductor if the area of cross section is increased?Answer:The resistance will decrease because the resistance has an in-direct relationship with the area. Where, ρ is the constant (resistivity of the material)Question 22.Why are copper and aluminium wires used for electrical transmission?Answer:Both copper and aluminium are good conductors of electricity, hence they are employed for electrical transmission.Question 23.What helps to maintain the potential difference across a conductor?Answer:The cell (battery eliminator) maintains the potential difference across a conductor.Question 24.Write one advantage of connecting devices in parallel and not in series.Answer:In parallel connection, if one device fails to work, others will continue working as the potential difference across parallel connection is same.Question 25.Give one difference between open circuit & closed circuit?Answer:In open circuit, no current can flow across the circuit. Whereas, in closed circuit, continuous current flows.

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