Chapter 14.2, Problem 1aT

How does the voltmeter reading compare to the potential difference across the electrodes? Explain.

If the sliding lead from electrode A were connected at point C along the resistor, would the voltmeter reading be positive, negative, or zero? Explain.

(Hint: Imagine disconnecting the ammeter and evacuated tube from the rest of the circuit, and answering the same question.)

How would you adjust the sliding connection from electrode A in order to make the potential difference across the electrodes $\left(△V_{BA}=V_A-V_B\right)$ become (i) more and more positive? (ii) more and more negative? Explain.

To determine

The potential difference reading in the voltmeter.

Voltmeter reading positive, negative or zero.

To adjustment to be made for the Voltmeter reading as positive and negative.

Answer to Problem 1aT

The potential across the electrodes is equal to the potential difference reading in the voltmeter.

Voltmeter reading will be positive.

By reversing the direction of the connection of the variable battery voltmeter can read negative potential.

Explanation of Solution

Introduction:

Photoelectric effect: Electrons from a metal surface are ejected when a light of an appropriate frequency is incident on it.The ejected electrons are called photoelectrons and the whole phenomenon is called photoelectric effect. This effect was explained by The Albert Einstein.

Figure 1 shows the circuit diagram to study the Photoelectric effect (PE).

  

Figure 1: Set up to study photoelectric effect

A monochromatic is incident on one of the electrodes ‘b’ . Electron bonded to a metal requires a minimum energy just to leave the surface of metal is called binding energy of electron, also known as work function of the electron and denoted as $\phi$ . If the energy ‘E’ of the incident wave is adequate enough to eject the electron from the electrode ‘b’ , these electrons are attracted towards the electrode ‘a’which is connected to the positive terminal of the of the battery. The voltmeter is connected parallel to the plates of the electrodes. Hence, the potential across the electrodes is equal to the potential difference reading in the voltmeter which depends on the battery connected to the circuit.

Current is flowing from positive to negative terminal of the battery (shown as red arrows in Figure 1).Therefore, the voltmeter will show the potential across electrode positive as electrons are flowing from high potential to lower potential.

Figure 2 shows the circuit diagram to study the Photoelectric effect (PE). In order to obtain the positive potentialdifference, read by voltmeter, figure 2(1) is applicable, as the electrode ‘b’ exposed to light is connected to negative terminal and other electrode ‘a’to the positive terminal of the battery. To make it more positive, one need to increase the potential of the variable battery that will make the electrode ‘a’more positive, hence will result in more positive potential across the electrodes.

  

Figure 2: Set up to study photoelectric effect

In order to obtain the negative potential difference,read by voltmeter, figure 2(2) is applicable, as the electrode ‘b’ exposed to light is connected to positive terminal and other electrode ‘a’to the negative terminal of the battery.

Conclusion:

The potential across the electrodes is equal to the potential difference reading in the voltmeter.Voltmeter reading will be positive.By reversing the direction of the connection of the variable battery voltmeter can read negative potential.