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Not to be confused with The Maternal Congruence or The Maternal Combustion.

"The Maternal Capacitance" is the fifteenth episode of the second season of the American sitcom The Big Bang Theory. This episode first aired on Monday, February 9, 2009.


Leonard's mother comes to visit. Her analytic nature drives everyone crazy except for Sheldon, giving Penny and Leonard common ground to get very close.

Extended Plot[]

The gang is playing “RockBand” with Raj singing, Howard is on drums and Sheldon is on guitar. Penny comes over to tell the guys to keep it down. While Leonard is busy on the telephone|phone, Sheldon theorizes that he has no relationship with the caller. It's his mother who is coming for a visit.

Penny is heading up The Stairs with laundry and meets a woman staring at The Elevator pondering the implications of how long the thing's broken. "You must be Leonard's mother,” remarks Penny. She replies "Well, I don't know if I must be, but yes." The woman introduces herself as Dr. Beverly Hofstadter. As they climb the stairs together, Penny starts to ask about Leonard as a child and learns about his penis grasping at age five. After Beverly learns that she is an actress she observes that, “There are many studies that suggest that people who go into the performing arts suffer from an external locus of identity." By the time they reach Leonard's apartment, she is in tears talking about her own childhood and trying to win her father's approval.

Leonard is not surprised by Penny's reaction as he invites his mother in. He makes tea for her to exact instructions just like Sheldon does, however, it was now cold. Beverly only had sex with her husband for procreation which they wrote papers about. Sheldon wants to hear more about her sex life. He can get the papers from the Princeton University Press; however, the PowerPoint slides are on her other laptop. Sheldon and Leonard debate about their mothers. Sheldon finds Beverly fascinating and Leonard had the childhood that he wanted.

The Maternal Capacitance 05

Lunch with Beverly.

At Caltech, Beverly is having lunch with the gang. After Howard asked, Beverly replied that, Leonard's two siblings are far more successful than he is. Dr. Hofstadter confirms that his younger brother, Michael, is a law professor teaching at Harvard University and his sister successfully grew a pancreas in an adolescent gibbon. “You must be very proud," replied Howard. "Why? They're not my accomplishments." Beverly leaves with Leonard telling them how hard they are making things on him. Upon her return Leonard tells her about Raj’s inability to talk to women and Howard living with his mother. "That's fascinating. Selective mutism is quite rare. On the other hand, a Jewish male living with his mother is so common, it borders on sociological cliche. You know, both selective mutism and an inability to separate from one's mother could be due to a pathological fear of women. That's would explain why the two of you have created an ersatz homosexual marriage to satisfy your need for intimacy." Howard denies it. At one o’clock she insists that Leonard show her his lab as he had promised even though he wants her to torture his friends. Describing his work as trying to reproduce the dark matter research performed by an Italian team, she tells him that she doesn't need to see his work, just get her a copy of their paper.

Leonard now could really use a drink, so he goes over to Penny's who is well ahead of him due to her analysis by Beverly. Beverly and Sheldon went to the hospital so that she could scan Sheldon's remarkable brain. Penny had also had not gotten an anti-depressant commercial because she was too perky. Leonard describes more of his miserable childhood and how he built a hugging machine which had two radio controlled arms just to have some human contact. Worse yet, his father used to borrow it.

The Maternal Capacitance 10

Penny and Leonard driven together by Leonard's mother.

Sheldon and Dr. Hofstadter return from the hospital and relax in his apartment. Sheldon seems to have developed quite the rapport with Dr. Hofstadter and is quite comfortable around her as is Beverly.

Penny and Leonard are feeling no pain downing tequila shots and are in a very good mood. She has him lick the salt off her neck, take a shot and bite the lime slice. He lingers on her neck, takes the shot and finds the lime in Penny's mouth. He goes after the lime and they start making out passionately.

Back in Apartment 4A, Beverly is contemplating Sheldon's "suggestion." She is not sure if it's appropriate with her son's roommate, but they both agree they'd be very good together.

The Maternal Capacitance 08

Sheldon and Beverly rocking out together.

Penny and Leonard have worked their way into bed. Leonard says that he can't believe it going to happen. She tell him to shush and he goes with "You know what my mother would say about this. She'd say because since you were not loved by your father and I was not loved by my mother that having sex is our way of making up for the intimacy we didn't get as children." This revelation stops Penny cold telling him that that is the sickest thing she has ever heard. Penny throws him out. After feeling terrible that he didn't keep his big mouth shut, he finds his mother and Sheldon using "Rock Band" doing "Any Way You Want It” with gusto.

However, in the morning, Penny wants to give Leonard an explanation and an apology for her actions, but Leonard understands what she is talking about and begs her never to talk of the night before ever again. Penny runs into Beverly when she is leaving and again is in tears by the time they reach the lobby. She wants Penny to have sessions with her, provided Penny is willing to go to New Jersey and go through a brain scan while doing so.



  • "Yet another consistent episode of comedy. You can’t help but laugh at the carefully crafted dialogue and attention to detail. But I can’t help but wonder what this show would be capable of with more characterization."[1] The TV Critic's Review
  • IMDb user reviews


  • Title Reference: Leonard's ability to handle his mother while she is visiting.
  • With 13.11 million viewers with a rating of 4.5 (adults 18–49). This episode was the most watched of the second season.
  • For all her intelligence and knowledge, Beverly seems to be completely unaware of the importance of reproducibility in science. Leonard says "I'm attempting to replicate the dark matter signal found in sodium iodide crystals by the Italians." (emphasis added) We're to understand that "the Italians" found a "dark matter signal" in sodium iodide crystals once and no one has been able to reproduce this result. This casts doubt on their result. If Leonard can either find the dark matter signal again or refute the Italian scientists' claims, it would be a major advance in the study of dark matter. Of course even if Beverly understands the importance of reproducibility in science, she still does not understand the importance of being supportive of her son's endeavors.
  • Chuck Lorre's vanity card.[2]
  • Episode transcript [1]

Costume Notes[]

The Maternal Capacitance 27 - Space Invaders

Space Invaders

The Maternal Capacitance 22

Atmospheric CO2

The Maternal Capacitance 23

BDG Earth Tones

Sheldon wears his orange Space Invaders tee, the Atmospheric CO2 shirt from Thinker Collection, and a discontinued Earth Tones pattern from Urban Outfitters.
The Maternal Capacitance 24

Out of This World

The Maternal Capacitance 25


The Maternal Capacitance 26

Periodic Table

Leonard wears his Out of This World shirt, a red periodic table shirt, an unknown graphic on a blue shirt, and the periodic table on a brown shirt.


  • First appearance of Beverly Hofstadter.
  • First episode where Leonard's brother and sister are mentioned.
  • In the first scene, Raj is singing Under the Bridge by The Red Hot Chili Peppers.
  • When assuming a number between 24 and 36 residents, based on the 16 mail boxes, Beverly uses a typical urban population density from 1.5 to 2.25 individuals per household.
  • When Sheldon notes that Leonard is the least successful of his siblings, Raj claims Leonard is the Jar Jar Binks of the Hofstadter family and Howard adopts Jar Jar's distinctive dialect to mock Leonard. Similarly, in "The 21-Second Excitation", Sheldon refers to Wil Wheaton as the Jar Jar Binks of the Star Trek universe and then Wil and Sheldon exchange quips while impersonating Jar Jar.
  • In the final scene, Beverly and Penny walk downstairs as Penny is leaving for work, and Beverly is going to the airport to go home. As they approach the first floor landing area, Penny says to Beverly (she's crying again and giving Beverly more information about her childhood and her issues), "My mom could have just said, 'Bob, get over it; she's a girl, move on'". This reveals that "Bob" is her Dad, but in "The Boyfriend Complexity", we are introduced to her father and his name is Wyatt.


[The gang, except for Leonard, are in the apartment's living room. Leonard enters the room, talking on his cell phone, and the gang overhear his side of the conversation.]
Leonard: I’m really very busy. Is there any way that we can put this off until I have more time to prepare? Of course. But, uh, you understand my trepidation.
Penny: What’s that about?
Howard: Not a clue.
Leonard: Can’t we just postpone it till the spring? Maybe next summer?
Sheldon: This should be fairly easy to deduce. He’s holding the phone to his left ear. Ears do not cross hemispheres, so he’s using the analytic rather than the emotional side of the brain, suggesting that he has no personal relationship with the caller.
Leonard: No, I didn't realize it had been so long. Sure, I guess there’s no other choice, but to just go ahead and do it.
Sheldon: He’s referring to an activity he has done before. It’s unpleasant and needs to be repeated. This suggests some sort of invasive medical test, like perhaps a colonoscopy.
Leonard: Aren't there any other options? There’s not a lot of room, it’s gonna be uncomfortable.
Sheldon: Yes, yes. I’m definitely going with colonoscopy.
Leonard: Okay, bye. [ends the call and turns to speak to the rest of the gang] My mother’s coming to visit.
Howard: [to Sheldon] How about that, you were right.

[After starting her laundry, Penny walks upstairs from the basement to the lobby. She notices a tall, bony woman with glasses, medium-length hair and a suitcase, staring at the elevator.]
Penny: It's out of order.
Woman: Yes, I can read the sign. I'm just pondering the implications.
Penny: I think it implies that the elevator doesn't work.
Woman: Again, I can read the sign. But the sign and the tape are covered with a layer of dust which indicates that the elevator has been non-functional for a significant amount of time which suggests either a remarkable passivity among the, I assume, 24 to 36 residents of this building based on the number of mailboxes and given typical urban population density, or a shared delusion of functionality.
[Penny stares at her a short while, until she realizes who she must be.]
Penny: You must be Leonard's mother.
Woman: Oh, I don't know if I must be, but yes.
Penny: Um, I'm Penny. I'm his neighbor.
Woman: Oh. Dr. Beverly Hofstadter.
Penny: Oh, nice to meet you. [Puts her hand out for Beverly to shake.]
Beverly: Oh, you're a hand shaker. Interesting.
Penny: Um, why don't you come with me. I'll walk you to the apartment.
Beverly: Oh, all right. Would you like to exchange pleasantries on the way?
Penny: Yeah, sure, I guess.
Beverly: All right, you start.
[They both walk up the stairs together.]
Penny: Okay. You know, I've always been curious. What was Leonard like when he was little?
Beverly: Oh, I think you mean young. He's always been little.
Penny: Right, Okay, what was he like he was young?
Beverly: You'll have to be more specific.
Penny: Oh, um... Okay, like, five or six.
[Beverly stares at her coldly.]
Penny: Five.
Beverly: Oh. Well, at that age, he was well enmeshed in what Freud would call the phallic stage of psychosexual development. An outmoded theory, of course, but the boy did spend most his waking hours with a tight grasp on his penis.
Penny: Oh yeah, Leonard mentioned you were a psychiatrist.
Beverly: Well, that is one of my degrees. My primary field is neuroscience.
Penny: Oh. Well, I'm an actress.
[There is a short silence between the two.]
Beverly: Why?
Penny: What do you mean, why?
Beverly: There are studies that suggest that many who go into the performing arts suffer from an external locus of identity.
Penny: Yeah, I don't know what that means.
Beverly: Well, it means you value yourself only as others value you, which is often the result of unmet childhood emotional needs.
Penny: Oh. Well, I had a wonderful childhood.
Beverly: Tell me about it.
[By the time they get to Leonard's and Sheldon's apartment, Penny is in absolute tears, talking about her dad.]
Penny: [sobbing] I know my dad wanted a boy! I, I just, I tried being good at sports, but I hated getting dirty!
Beverly: And then I'm assuming you entered adolescence.
Penny: Uh-huh, he called me Slugger until I got my first training bra and then he just stopped playing catch with me! I wasn't Slugger anymore!
[Penny knocks on the apartment door and Leonard answers.]
Penny: [to Leonard, as she gives vent to a huge sob] Your mother's here!
[Penny, still crying, goes to her apartment.]
Beverly: [to Leonard] If you want to have intercourse with that girl, find out what kind of cologne her father wore.
Leonard: Good to see you, Mother.

[Leonard's mother Beverly has just arrived at the apartment.]
Leonard: Here's your tea, Mother.
Beverly: Oolong?
Leonard: Yes.
Beverly: Loose, not bagged?
Leonard: Yes.
Beverly: Steeped 3 minutes?
Leonard: Yes.
Beverly: 2% milk?
Leonard: Yes.
Beverly: Warmed separately?
Leonard: Yes.
Beverly: One teaspoon of sugar?
Leonard: Yes.
Beverly: Raw sugar?
Leonard: Yes.
[Beverly takes a sip.]
Beverly: It's cold.
Leonard: I'll start again. [He goes to the kitchen.]
Sheldon: I have the same problem with him. My theory is that his lack of focus stems from an overdeveloped sex drive.
Beverly: Oh, I don’t know where he would've gotten that. Aside from a pro forma consummation of our marriage, his father and I only had intercourse for the purposes of reproduction.
Sheldon: That seems a fairly efficient arrangement.
Beverly: Yes, we think so. We've both done papers on it. Mine from the neuroscientific point of view and his from an anthropological. Mine, of course, was the only one worth reading.
Sheldon: Of course. I would very much like to read about your sex life.
Beverly: Well, it’s all online, or you can order it from the Princeton University Press.

[Leonard returns from the kitchen.]
Leonard: So, Mother, what’s new?
Beverly: You’ll have to be more specific.
Leonard: All right. Uh, what’s new with you?
Beverly: Oh. Well, I've been having some fascinating menopausal symptoms recently.
Leonard: Maybe something less personal.
Beverly: Oh. [matter-of-fact'ly] Your Uncle Floyd died.
Leonard: Oh, my God. What happened?
Beverly: His heart stopped beating. [abruptly stands up] I have to urinate. [She heads for the bathroom.]
Sheldon: What a remarkable woman.
Leonard: Yeah, I thought you guys might hit it off.
Sheldon: I envy you your childhood.
Leonard: I hate to tell you, but the only warm memories I have of my childhood are of my Uncle Floyd.
Sheldon: You’re clearly misremembering. Your mother is brilliant, analytic, insightful, and I’m betting she never hit you with a Bible because you wouldn't eat your Brussels sprouts.
Leonard: Sheldon, you don’t give your mother enough credit. She’s warm, she’s loving, she doesn't glue electrodes to your head to measure your brain waves while potty training.
Sheldon: You were lucky. When I was a kid, if I wanted an EEG, I had to attach my own electrodes.

[At the university cafeteria, Beverly joins the guys for lunch.]
Howard: So, Dr. Hofstadter, Leonard rarely talks about his incredibly successful brother and sister.
Leonard: Please, don’t go there, Howard.
Howard: I understand that unlike Leonard, they’re at the top of their respective fields.
Leonard: Boy, you suck.
Beverly: Well, Leonard’s younger brother, Michael, is a tenured law professor at Harvard, and his sister just successfully grew a human pancreas in an adolescent gibbon.
Howard: So, she’s close to curing diabetes?
Beverly: Why else would you grow a pancreas in a teen-aged gibbon?
Howard: Wow. You must be very proud.
Beverly: Why? They’re not my accomplishments. [abruptly stands up] I have to urinate. [She heads for the bathroom.]
Leonard: Why are you doing this?
Howard: You know the rules. You brought your mom to work, you must suffer.
Sheldon: Leonard, I had no idea your siblings were so much more successful than you.
Raj: Yeah, you’re like the Jar Jar Binks of the Hofstadter family.
Howard: [doing Jar Jar Binks impression] Oh, meesa think yousa lookin’ so so sad.
Leonard: You know, rather than mock me, my friends might realize that this is difficult and try to help me through it.
Raj: Nope, I think mocking you is more fun.
Howard: Next time, don’t yousa bring mama to work. Okee-day?

[Beverly returns from the bathroom.]
Leonard: That was fast.
Beverly: Oh, the middle stall was occupied. I’ll have to try again later.
Sheldon: It’s totally understandable. In bladder voiding, as in real estate, it's location, location, location.
Beverly: So, where were we?
Leonard: Howard lives with his mother and Raj can’t speak to women unless he’s drunk. Go!
Beverly: That’s fascinating. Selective mutism is quite rare. On the other hand, an adult Jewish male living with his mother is so common it borders on sociological cliche.
Howard: It’s just temporary. I pay rent.
Leonard: He lives in the same room where his bassinet was.
Beverly: You know, both selective mutism and an inability to separate from one’s mother can stem from a pathological fear of women. It might explain why the two of you have created an ersatz homosexual marriage to satisfy your need for intimacy.
[Leonard has a huge smile on his face]
Howard: Say what? [Raj whispers in his ear] That’s basically what I just said!
Leonard: You brought your husband to work, you know the rules. [doing Jar Jar Binks impression] Meesa thinkin' yousa lookin' pretty sad now too, betcha, betcha.
[Howard and Raj are disgusted and pissed]

[Beverly and Leonard go to Leonard's laboratory, leaving Howard, Raj and Sheldon at the table.]
Howard: Just for the record, we’re not in an ersatz homosexual relationship.
Raj: Well, then why didn't you say that to her?
Howard: Why is it always my responsibility?
Raj: It’s not always your responsibility. I swear, this is the same thing you did at the comic book store last week.
Howard: I can’t believe you’re bringing that up.
Raj: I didn't bring it up. You did.
Howard: [annoyed] We’ll talk about this later.
Raj: You always say that, but we never do!
[Following this exchange, Sheldon sits in silence for several seconds. Then ...]
Sheldon: You went to the comic book store without me?

[Leonard knocks on Penny's apartment door. Penny answers.]
Penny: Hey.
Leonard: You got alcohol?
Penny: Your mom still here?
Leonard: Yep.
Penny: Come on in. Wait, wait. She’s not gonna come here looking for you, is she?
Leonard: Oh, relax. She took Sheldon to the hospital to get a brain scan.
Penny: Oh, my God. What happened?
Leonard: Nothing. Mother likes looking at brains and Sheldon likes getting his brain scanned.
Penny: Geez, what a fun couple. [She pours Leonard a glass of wine.]
Leonard: She’s only been here a day and a half and I’m seriously considering alcoholism as a new career path.
Penny: Hey, I talked to her for five minutes yesterday and I've been half bombed ever since.
Leonard: You can’t let her get into your head.
Penny: My head? What about yours?
Leonard: It’s too late for me. My head is her summer house.
Penny: She was right, you know. The locus of my identity is totally exterior to me.
Leonard: [looking at Penny's head] Oh, yeah, there she is. Hi, Mom.
Penny: I mean, do you know where I was all morning? Auditioning with fifty other blondes for some stupid antidepressant commercial. And for what? So I’ll finally get my daddy’s approval?
Leonard: Did you get the part?
Penny: No, [starts crying] they said I was too perky!
Leonard: Hey, you want to talk about not getting love from a parent. You know what I used to do when I was little to have some sensation of human contact?
Penny: Yeah, you grabbed your penis and wouldn't let go. [Leonard looks shocked] Your mother told me.
Leonard: [annoyed] Of course she did. Anyway, that’s not what I was gonna say. When I was ten years old, I built a hugging machine.
Penny: A hugging machine?
Leonard: Yeah. I got a dressmaker’s mannequin, I stuffed it with an electric blanket so it would be warm, and built two radio-controlled arms that would hug me and pat my back.
Penny: Oh, that is so sad.
Leonard: You know what the saddest part was?
Penny: What?
Leonard: My father used to borrow it.

[Sheldon and Beverly return from the hospital. As they walk up the stairs, they look at the images from Sheldon's brain scan.]
Beverly: Your scan data will be very helpful to my research. You have a remarkable brain.
Sheldon: I know. Although I've always hated how my right frontal lobe looks in pictures.
Beverly: Common complaint among men. Nothing’s ever big enough, except when they get a tumor. Then you never hear the end of it.
Sheldon: I’d love to see a scan of your brain sometime.
Beverly: I’ll send you a link, but its physiology is fairly unimpressive.
Sheldon: Oh, I can’t believe that.
Beverly: Your unwillingness to accept empirical evidence suggests an attempt at flattery.
Sheldon: My apologies. I've been living with your son too long. Gotten into some bad habits.
Beverly: Understandable.
Sheldon: Can I make you a cup of tea?
Beverly: I doubt it, but if anyone has a chance, it’s probably you.
Sheldon: I feel very comfortable around you.
Beverly: I feel very comfortable around you, too.
Sheldon: It’s surprising because I generally don’t feel comfortable around, well, anyone.
Beverly: Nor I.
Sheldon: What are the odds that two individuals as unique as ourselves would be connected by someone as comparatively workaday as your son?
Beverly: Is that a rhetorical point or would you like to do the math?
Sheldon: I’d like to do the math.
Beverly: I’d like that, too.

[In Penny's apartment, Leonard and Penny have switched from wine to tequila shots.]
Penny: You’re gonna lick the salt off my neck, do the shot, and then bite the lime. [She sprinkles salt on her neck.]
Leonard: [drunkenly] I’m sorry, I didn't hear anything after lick.
Penny: [pointing to each item in sequence] Neck, shot, lime.
[Leonard licks the salt off of Penny's neck, taking his time about it. After several seconds, Penny decides it's been long enough.]
Penny: Okay. Shot, lime.
Leonard: Right. [does the shot] Ah! Where’s the lime?
[Penny grins, revealing that she has the lime clenched in her teeth.]
Leonard: Oh. Okay, we’re sharing.
[Leonard leans close to Penny to bite the lime. Inevitably, they end up kissing. After a few seconds, Leonard breaks off the kiss, turns away from Penny, spits out the lime, and then returns to kissing her.]

[Meanwhile, in Sheldon's and Leonard's apartment, Beverly and Sheldon are deep in thought.]
Sheldon: So, what do you think?
Beverly: I’m very tempted. I’m just not sure it’s appropriate with my son’s roommate.
Sheldon: Normally, I’d feel the same way. But based on everything I've observed about us, I can’t help but speculate we’d be very good together.
Beverly: True. I've had a similar observation. It’s certainly something I could never do with my husband.
Sheldon: I was hesitant the first time I tried it, but I experienced an unanticipated and remarkable release of endorphins. It’s quite satisfying.
Beverly: [smiling] I see what you’re doing. You’re appealing to the neuroscientific researcher in me.
Sheldon: You see right through me, don’t you?
Beverly: Only when you’re in a CAT scanner.

[Back in Penny's apartment, Leonard and Penny are in Penny's bed. Their rendezvous has obviously gotten more heated, as Penny has removed her shirt and is now in her bra.]
Leonard: This is actually gonna happen.
Penny: Honey, shush. Shush, shush, shush, shush.
Leonard: You shush. I’m happy, I want to talk about it. You know what my mother would say about this? She would say because you were not loved by your father and I was not loved by my mother, that having sex is our way of making up for the intimacy we didn't get as children.
Penny: [annoyed] Why would you bring that up right now?
Leonard: I don’t know. Foreplay?
Penny: So you’re saying you’re not having sex with me, you’re having sex with your mother?
Leonard: Ummm, I’m gonna go with "no".
Penny: That is the sickest thing I've ever heard.
Leonard: Come on. You’re trying to have sex with your father, and I’m okay with that.
[The scene abruptly shifts to Penny's front door. Leonard is being bodily pushed out the door and into the hallway.]
Penny: [from inside her apartment] GET OUT!
Leonard: She said shush. I should have shushed.
[He goes back into his own apartment, where loud music is playing. He is then befuddled at the sight of Sheldon and Beverly completely absorbed in a jam session, using a karaoke machine to perform a duet of Journey's "Any Way You Want It".]

[The next morning, Beverly is leaving. She and Leonard are saying their goodbyes in the hallway.]
Leonard: All right, Mother. Um, have a nice flight.
Beverly: That’s not really in my control, is it? Oh, uh, yes. [She gives him a stiff and obviously uncomfortable hug.]
[Penny comes out of her apartment dressed in her waitress uniform, evidently on her way to work.]
Penny: Oh, good morning.
Leonard: Morning.
Penny: Look, I was just coming over to talk to you.
Leonard: You don’t have to. Ever. [They exchange a meaningful look of understanding.]
Penny: Gotcha.
Leonard: [to Beverly] Goodbye, Mother.
Beverly: Goodbye, Leonard. [to Penny] So, Slugger, shall we pick up where we left off last time?
[Beverly and Penny begin walking down the stairs. By the time they reach the lobby, Penny is in tears again.]
Penny: [sobbing] I mean, my mom could've just said, "Bob, get over it! She's a girl! Move on!" But she didn't, not one word!
Beverly: Interesting. Would you be willing to fly to New Jersey and discuss your relationship with your parents during a brain scan?
Penny: Would it help?
Beverly: Well, it would help me.