A Hall-effect probe to measure magnetic field strengths needs to be calibrated in a known magnetic field. Although it is not easy to do, magnetic fields can be precisely measured by measuring the cyclotron frequency of protons. A testing laboratory adjusts a magnetic field until the protons cyclotron frequency is 10.0 MHz. At this field strength, the Hall voltage on the probe is 0.543 mV when the current through the probe is 0.150 mA. Later, when an unknown magnetic field is measured, the Hall voltage at the same current is 1.735 mV. What is the strength of this magnetic field?
3-‐29-‐16 Motivation II. Psychological View of Obesity • One psychological approach to understanding obesity comes from the work of Stanley Schacter • Called Internal/External Theory o Schacter proposed that obese people eat not only when they are hungry, but also when the correct environmental cues are present. § Ex. Eating at lunch time when not hungry, eating at 2 when hungry § Obese individuals will nearly always engage in eating behavior if and when: § Food is viewed (ex. Tv commercial/buffet) § The correct eating time arrives (ex. noon § He called these people, “externals” o Of course, people of normal weight tend to eat only when the correct internal cues are present (ex. when they get hunger pangs) o He called these people “internals” o Schacter conducted a series of about 20 studies.. § In one study, normal weight and obese people were asked to sit at a table and fill out a questionnaire § The experimenter left a bag of almonds on the desk and invited subjects to help themselves while they were filling out the questions § In condition #1: shells were off the nuts § In condition #2: shells were left on the nuts (nutcracker was provided) § When subjects left the room, the nuts were counted to determine who had eaten any § Results: • Shells on: Normal Weight: 50% Obese Weight: 5% • Shells off: Normal Weight: 50% Obese Weight: 95% § Conclusion: • Obese people eat more than normal people when: o Food is present o When it is easy to get § Evidence also shows that the more salient (visually obvious) the food cue is, the more likely it will lead to eating behavior for externals. § For example, researchers have shown that… • Obese people will eat far more from a bowl of nuts when the bowl is brightly illuminated than when it is dimly lit. (buffet trays) • For normal weight individuals, the illumination had no effect on eating behavior. • In sum, the current theories suggest that both physiological and psychological factors contribute to human obesity.